What's the fastest way to convert String to Number in JavaScript? - javascript

Any number, it's number. String looks like a number, it's number. Everything else, it goes NaN.
'a' => NaN
'1' => 1
1 => 1

There are 4 ways to do it as far as I know.
Number(x);
parseInt(x, 10);
parseFloat(x);
+x;
By this quick test I made, it actually depends on browsers.
https://jsben.ch/NnBKM
Implicit marked the fastest on 3 browsers, but it makes the code hard to read… So choose whatever you feel like it!

There are at least 5 ways to do this:
If you want to convert to integers only, another fast (and short) way is the double-bitwise not (i.e. using two tilde characters):
e.g.
~~x;
Reference: http://james.padolsey.com/cool-stuff/double-bitwise-not/
The 5 common ways I know so far to convert a string to a number all have their differences (there are more bitwise operators that work, but they all give the same result as ~~). This JSFiddle shows the different results you can expect in the debug console: http://jsfiddle.net/TrueBlueAussie/j7x0q0e3/22/
var values = ["123",
undefined,
"not a number",
"123.45",
"1234 error",
"2147483648",
"4999999999"
];
for (var i = 0; i < values.length; i++){
var x = values[i];
console.log(x);
console.log(" Number(x) = " + Number(x));
console.log(" parseInt(x, 10) = " + parseInt(x, 10));
console.log(" parseFloat(x) = " + parseFloat(x));
console.log(" +x = " + +x);
console.log(" ~~x = " + ~~x);
}
Debug console:
123
Number(x) = 123
parseInt(x, 10) = 123
parseFloat(x) = 123
+x = 123
~~x = 123
undefined
Number(x) = NaN
parseInt(x, 10) = NaN
parseFloat(x) = NaN
+x = NaN
~~x = 0
null
Number(x) = 0
parseInt(x, 10) = NaN
parseFloat(x) = NaN
+x = 0
~~x = 0
"not a number"
Number(x) = NaN
parseInt(x, 10) = NaN
parseFloat(x) = NaN
+x = NaN
~~x = 0
123.45
Number(x) = 123.45
parseInt(x, 10) = 123
parseFloat(x) = 123.45
+x = 123.45
~~x = 123
1234 error
Number(x) = NaN
parseInt(x, 10) = 1234
parseFloat(x) = 1234
+x = NaN
~~x = 0
2147483648
Number(x) = 2147483648
parseInt(x, 10) = 2147483648
parseFloat(x) = 2147483648
+x = 2147483648
~~x = -2147483648
4999999999
Number(x) = 4999999999
parseInt(x, 10) = 4999999999
parseFloat(x) = 4999999999
+x = 4999999999
~~x = 705032703
The ~~x version results in a number in "more" cases, where others often result in undefined, but it fails for invalid input (e.g. it will return 0 if the string contains non-number characters after a valid number).
Overflow
Please note: Integer overflow and/or bit truncation can occur with ~~, but not the other conversions. While it is unusual to be entering such large values, you need to be aware of this. Example updated to include much larger values.
Some Perf tests indicate that the standard parseInt and parseFloat functions are actually the fastest options, presumably highly optimised by browsers, but it all depends on your requirement as all options are fast enough: http://jsperf.com/best-of-string-to-number-conversion/37
This all depends on how the perf tests are configured as some show parseInt/parseFloat to be much slower.
My theory is:
Lies
Darn lines
Statistics
JSPerf results :)

Prefix the string with the + operator.
console.log(+'a') // NaN
console.log(+'1') // 1
console.log(+1) // 1

A fast way to convert strings to an integer is to use a bitwise or, like so:
x | 0
While it depends on how it is implemented, in theory it should be relatively fast (at least as fast as +x) since it will first cast x to a number and then perform a very efficient or.

Here is simple way to do it: var num = Number(str); in this example str is the variable that contains the string.
You can tested and see how it works open: Google chrome developer tools, then go to the console and paste the following code.
read the comments to understand better how the conversion is done.
// Here Im creating my variable as a string
var str = "258";
// here im printing the string variable: str
console.log ( str );
// here Im using typeof , this tells me that the variable str is the type: string
console.log ("The variable str is type: " + typeof str);
// here is where the conversion happens
// Number will take the string in the parentesis and transform it to a variable num as type: number
var num = Number(str);
console.log ("The variable num is type: " + typeof num);

I find that num * 1 is simple, clear, and works for integers and floats...

This is probably not that fast, but has the added benefit of making sure your number is at least a certain value (e.g. 0), or at most a certain value:
Math.max(input, 0);
If you need to ensure a minimum value, usually you'd do
var number = Number(input);
if (number < 0) number = 0;
Math.max(..., 0) saves you from writing two statements.

7 ways to convert a String to Number:
let str = "43.2"
1. Number(str) => 43.2
2. parseInt(str) => 43
3. parseFloat(str) => 43.2
4. +str => 43
5. str * 1 => 43.2
6. Math.floor(str) => 43
7. ~~str => 43

You can try using UnitOf, a measurement and data type conversion library we just officially released! UnitOf is super fast, small in size, and efficient at converting any data type without ever throwing an error or null/undefined. Default values you define or UnitOf's defaults are returned when a conversion is unsuccessful.
//One liner examples
UnitOf.DataType("12.5").toFloat(); //12.5 of type Float is returned. 0 would be returned if conversion failed.
UnitOf.DataType("Not A Num").toInt(10); //10 of type Int is returned as the conversion failed.
//Or as a variable
var unit = UnitOf.DataType("12.5");
unit.toInt(5); //12.5 of type Float is returned. 5 would be returned if the conversion failed.
unit.toFloat(8); // 12 of type Int is returned. 8 would be returned if the conversion failed.

The fastest way is using -0:
const num = "12.34" - 0;

Related

Decrement loop in javascript [duplicate]

How do I convert a string to an integer in JavaScript?
The simplest way would be to use the native Number function:
var x = Number("1000")
If that doesn't work for you, then there are the parseInt, unary plus, parseFloat with floor, and Math.round methods.
parseInt()
var x = parseInt("1000", 10); // You want to use radix 10
// So you get a decimal number even with a leading 0 and an old browser ([IE8, Firefox 20, Chrome 22 and older][1])
Unary plus
If your string is already in the form of an integer:
var x = +"1000";
floor()
If your string is or might be a float and you want an integer:
var x = Math.floor("1000.01"); // floor() automatically converts string to number
Or, if you're going to be using Math.floor several times:
var floor = Math.floor;
var x = floor("1000.01");
parseFloat()
If you're the type who forgets to put the radix in when you call parseInt, you can use parseFloat and round it however you like. Here I use floor.
var floor = Math.floor;
var x = floor(parseFloat("1000.01"));
round()
Interestingly, Math.round (like Math.floor) will do a string to number conversion, so if you want the number rounded (or if you have an integer in the string), this is a great way, maybe my favorite:
var round = Math.round;
var x = round("1000"); // Equivalent to round("1000", 0)
Try parseInt function:
var number = parseInt("10");
But there is a problem. If you try to convert "010" using parseInt function, it detects as octal number, and will return number 8. So, you need to specify a radix (from 2 to 36). In this case base 10.
parseInt(string, radix)
Example:
var result = parseInt("010", 10) == 10; // Returns true
var result = parseInt("010") == 10; // Returns false
Note that parseInt ignores bad data after parsing anything valid.
This guid will parse as 51:
var result = parseInt('51e3daf6-b521-446a-9f5b-a1bb4d8bac36', 10) == 51; // Returns true
There are two main ways to convert a string to a number in JavaScript. One way is to parse it and the other way is to change its type to a Number. All of the tricks in the other answers (e.g., unary plus) involve implicitly coercing the type of the string to a number. You can also do the same thing explicitly with the Number function.
Parsing
var parsed = parseInt("97", 10);
parseInt and parseFloat are the two functions used for parsing strings to numbers. Parsing will stop silently if it hits a character it doesn't recognise, which can be useful for parsing strings like "92px", but it's also somewhat dangerous, since it won't give you any kind of error on bad input, instead you'll get back NaN unless the string starts with a number. Whitespace at the beginning of the string is ignored. Here's an example of it doing something different to what you want, and giving no indication that anything went wrong:
var widgetsSold = parseInt("97,800", 10); // widgetsSold is now 97
It's good practice to always specify the radix as the second argument. In older browsers, if the string started with a 0, it would be interpreted as octal if the radix wasn't specified which took a lot of people by surprise. The behaviour for hexadecimal is triggered by having the string start with 0x if no radix is specified, e.g., 0xff. The standard actually changed with ECMAScript 5, so modern browsers no longer trigger octal when there's a leading 0 if no radix has been specified. parseInt understands radixes up to base 36, in which case both upper and lower case letters are treated as equivalent.
Changing the Type of a String to a Number
All of the other tricks mentioned above that don't use parseInt, involve implicitly coercing the string into a number. I prefer to do this explicitly,
var cast = Number("97");
This has different behavior to the parse methods (although it still ignores whitespace). It's more strict: if it doesn't understand the whole of the string than it returns NaN, so you can't use it for strings like 97px. Since you want a primitive number rather than a Number wrapper object, make sure you don't put new in front of the Number function.
Obviously, converting to a Number gives you a value that might be a float rather than an integer, so if you want an integer, you need to modify it. There are a few ways of doing this:
var rounded = Math.floor(Number("97.654")); // other options are Math.ceil, Math.round
var fixed = Number("97.654").toFixed(0); // rounded rather than truncated
var bitwised = Number("97.654")|0; // do not use for large numbers
Any bitwise operator (here I've done a bitwise or, but you could also do double negation as in an earlier answer or a bit shift) will convert the value to a 32 bit integer, and most of them will convert to a signed integer. Note that this will not do want you want for large integers. If the integer cannot be represented in 32 bits, it will wrap.
~~"3000000000.654" === -1294967296
// This is the same as
Number("3000000000.654")|0
"3000000000.654" >>> 0 === 3000000000 // unsigned right shift gives you an extra bit
"300000000000.654" >>> 0 === 3647256576 // but still fails with larger numbers
To work correctly with larger numbers, you should use the rounding methods
Math.floor("3000000000.654") === 3000000000
// This is the same as
Math.floor(Number("3000000000.654"))
Bear in mind that coercion understands exponential notation and Infinity, so 2e2 is 200 rather than NaN, while the parse methods don't.
Custom
It's unlikely that either of these methods do exactly what you want. For example, usually I would want an error thrown if parsing fails, and I don't need support for Infinity, exponentials or leading whitespace. Depending on your use case, sometimes it makes sense to write a custom conversion function.
Always check that the output of Number or one of the parse methods is the sort of number you expect. You will almost certainly want to use isNaN to make sure the number is not NaN (usually the only way you find out that the parse failed).
ParseInt() and + are different
parseInt("10.3456") // returns 10
+"10.3456" // returns 10.3456
Fastest
var x = "1000"*1;
Test
Here is little comparison of speed (macOS only)... :)
For Chrome, 'plus' and 'mul' are fastest (>700,000,00 op/sec), 'Math.floor' is slowest. For Firefox, 'plus' is slowest (!) 'mul' is fastest (>900,000,000 op/sec). In Safari 'parseInt' is fastest, 'number' is slowest (but results are quite similar, >13,000,000 <31,000,000). So Safari for cast string to int is more than 10x slower than other browsers. So the winner is 'mul' :)
You can run it on your browser by this link
https://jsperf.com/js-cast-str-to-number/1
I also tested var x = ~~"1000";. On Chrome and Safari, it is a little bit slower than var x = "1000"*1 (<1%), and on Firefox it is a little bit faster (<1%).
I use this way of converting string to number:
var str = "25"; // String
var number = str*1; // Number
So, when multiplying by 1, the value does not change, but JavaScript automatically returns a number.
But as it is shown below, this should be used if you are sure that the str is a number (or can be represented as a number), otherwise it will return NaN - not a number.
You can create simple function to use, e.g.,
function toNumber(str) {
return str*1;
}
Try parseInt.
var number = parseInt("10", 10); //number will have value of 10.
I love this trick:
~~"2.123"; //2
~~"5"; //5
The double bitwise negative drops off anything after the decimal point AND converts it to a number format. I've been told it's slightly faster than calling functions and whatnot, but I'm not entirely convinced.
Another method I just saw here (a question about the JavaScript >>> operator, which is a zero-fill right shift) which shows that shifting a number by 0 with this operator converts the number to a uint32 which is nice if you also want it unsigned. Again, this converts to an unsigned integer, which can lead to strange behaviors if you use a signed number.
"-2.123" >>> 0; // 4294967294
"2.123" >>> 0; // 2
"-5" >>> 0; // 4294967291
"5" >>> 0; // 5
In JavaScript, you can do the following:
ParseInt
parseInt("10.5") // Returns 10
Multiplying with 1
var s = "10";
s = s*1; // Returns 10
Using the unary operator (+)
var s = "10";
s = +s; // Returns 10
Using a bitwise operator
(Note: It starts to break after 2140000000. Example: ~~"2150000000" = -2144967296)
var s = "10.5";
s = ~~s; // Returns 10
Using Math.floor() or Math.ceil()
var s = "10";
s = Math.floor(s) || Math.ceil(s); // Returns 10
Please see the below example. It will help answer your question.
Example Result
parseInt("4") 4
parseInt("5aaa") 5
parseInt("4.33333") 4
parseInt("aaa"); NaN (means "Not a Number")
By using parseint function, it will only give op of integer present and not the string.
Beware if you use parseInt to convert a float in scientific notation!
For example:
parseInt("5.6e-14")
will result in
5
instead of
0
Also as a side note: MooTools has the function toInt() which is used on any native string (or float (or integer)).
"2".toInt() // 2
"2px".toInt() // 2
2.toInt() // 2
We can use +(stringOfNumber) instead of using parseInt(stringOfNumber).
Example: +("21") returns int of 21, like the parseInt("21").
We can use this unary "+" operator for parsing float too...
To convert a String into Integer, I recommend using parseFloat and not parseInt. Here's why:
Using parseFloat:
parseFloat('2.34cms') //Output: 2.34
parseFloat('12.5') //Output: 12.5
parseFloat('012.3') //Output: 12.3
Using parseInt:
parseInt('2.34cms') //Output: 2
parseInt('12.5') //Output: 12
parseInt('012.3') //Output: 12
So if you have noticed parseInt discards the values after the decimals, whereas parseFloat lets you work with floating point numbers and hence more suitable if you want to retain the values after decimals. Use parseInt if and only if you are sure that you want the integer value.
There are many ways in JavaScript to convert a string to a number value... All are simple and handy. Choose the way which one works for you:
var num = Number("999.5"); //999.5
var num = parseInt("999.5", 10); //999
var num = parseFloat("999.5"); //999.5
var num = +"999.5"; //999.5
Also, any Math operation converts them to number, for example...
var num = "999.5" / 1; //999.5
var num = "999.5" * 1; //999.5
var num = "999.5" - 1 + 1; //999.5
var num = "999.5" - 0; //999.5
var num = Math.floor("999.5"); //999
var num = ~~"999.5"; //999
My prefer way is using + sign, which is the elegant way to convert a string to number in JavaScript.
Try str - 0 to convert string to number.
> str = '0'
> str - 0
0
> str = '123'
> str - 0
123
> str = '-12'
> str - 0
-12
> str = 'asdf'
> str - 0
NaN
> str = '12.34'
> str - 0
12.34
Here are two links to compare the performance of several ways to convert string to int
https://jsperf.com/number-vs-parseint-vs-plus
http://phrogz.net/js/string_to_number.html
Here is the easiest solution
let myNumber = "123" | 0;
More easy solution
let myNumber = +"123";
In my opinion, no answer covers all edge cases as parsing a float should result in an error.
function parseInteger(value) {
if(value === '') return NaN;
const number = Number(value);
return Number.isInteger(number) ? number : NaN;
}
parseInteger("4") // 4
parseInteger("5aaa") // NaN
parseInteger("4.33333") // NaN
parseInteger("aaa"); // NaN
The easiest way would be to use + like this
const strTen = "10"
const numTen = +strTen // string to number conversion
console.log(typeof strTen) // string
console.log(typeof numTen) // number
I actually needed to "save" a string as an integer, for a binding between C and JavaScript, so I convert the string into an integer value:
/*
Examples:
int2str( str2int("test") ) == "test" // true
int2str( str2int("t€st") ) // "t¬st", because "€".charCodeAt(0) is 8364, will be AND'ed with 0xff
Limitations:
maximum 4 characters, so it fits into an integer
*/
function str2int(the_str) {
var ret = 0;
var len = the_str.length;
if (len >= 1) ret += (the_str.charCodeAt(0) & 0xff) << 0;
if (len >= 2) ret += (the_str.charCodeAt(1) & 0xff) << 8;
if (len >= 3) ret += (the_str.charCodeAt(2) & 0xff) << 16;
if (len >= 4) ret += (the_str.charCodeAt(3) & 0xff) << 24;
return ret;
}
function int2str(the_int) {
var tmp = [
(the_int & 0x000000ff) >> 0,
(the_int & 0x0000ff00) >> 8,
(the_int & 0x00ff0000) >> 16,
(the_int & 0xff000000) >> 24
];
var ret = "";
for (var i=0; i<4; i++) {
if (tmp[i] == 0)
break;
ret += String.fromCharCode(tmp[i]);
}
return ret;
}
String to Number in JavaScript:
Unary + (most recommended)
+numStr is easy to use and has better performance compared with others
Supports both integers and decimals
console.log(+'123.45') // => 123.45
Some other options:
Parsing Strings:
parseInt(numStr) for integers
parseFloat(numStr) for both integers and decimals
console.log(parseInt('123.456')) // => 123
console.log(parseFloat('123')) // => 123
JavaScript Functions
Math functions like round(numStr), floor(numStr), ceil(numStr) for integers
Number(numStr) for both integers and decimals
console.log(Math.floor('123')) // => 123
console.log(Math.round('123.456')) // => 123
console.log(Math.ceil('123.454')) // => 124
console.log(Number('123.123')) // => 123.123
Unary Operators
All basic unary operators, +numStr, numStr-0, 1*numStr, numStr*1, and numStr/1
All support both integers and decimals
Be cautious about numStr+0. It returns a string.
console.log(+'123') // => 123
console.log('002'-0) // => 2
console.log(1*'5') // => 5
console.log('7.7'*1) // => 7.7
console.log(3.3/1) // =>3.3
console.log('123.123'+0, typeof ('123.123' + 0)) // => 123.1230 string
Bitwise Operators
Two tilde ~~numStr or left shift 0, numStr<<0
Supports only integers, but not decimals
console.log(~~'123') // => 123
console.log('0123'<<0) // => 123
console.log(~~'123.123') // => 123
console.log('123.123'<<0) // => 123
// Parsing
console.log(parseInt('123.456')) // => 123
console.log(parseFloat('123')) // => 123
// Function
console.log(Math.floor('123')) // => 123
console.log(Math.round('123.456')) // => 123
console.log(Math.ceil('123.454')) // => 124
console.log(Number('123.123')) // => 123.123
// Unary
console.log(+'123') // => 123
console.log('002'-0) // => 2
console.log(1*'5') // => 5
console.log('7.7'*1) // => 7.7
console.log(3.3/1) // => 3.3
console.log('123.123'+0, typeof ('123.123'+0)) // => 123.1230 string
// Bitwise
console.log(~~'123') // => 123
console.log('0123'<<0) // => 123
console.log(~~'123.123') // => 123
console.log('123.123'<<0) // => 123
function parseIntSmarter(str) {
// ParseInt is bad because it returns 22 for "22thisendsintext"
// Number() is returns NaN if it ends in non-numbers, but it returns 0 for empty or whitespace strings.
return isNaN(Number(str)) ? NaN : parseInt(str, 10);
}
You can use plus.
For example:
var personAge = '24';
var personAge1 = (+personAge)
then you can see the new variable's type bytypeof personAge1 ; which is number.
Summing the multiplication of digits with their respective power of ten:
i.e: 123 = 100+20+3 = 1100 + 2+10 + 31 = 1*(10^2) + 2*(10^1) + 3*(10^0)
function atoi(array) {
// Use exp as (length - i), other option would be
// to reverse the array.
// Multiply a[i] * 10^(exp) and sum
let sum = 0;
for (let i = 0; i < array.length; i++) {
let exp = array.length - (i+1);
let value = array[i] * Math.pow(10, exp);
sum += value;
}
return sum;
}
The safest way to ensure you get a valid integer:
let integer = (parseInt(value, 10) || 0);
Examples:
// Example 1 - Invalid value:
let value = null;
let integer = (parseInt(value, 10) || 0);
// => integer = 0
// Example 2 - Valid value:
let value = "1230.42";
let integer = (parseInt(value, 10) || 0);
// => integer = 1230
// Example 3 - Invalid value:
let value = () => { return 412 };
let integer = (parseInt(value, 10) || 0);
// => integer = 0
Another option is to double XOR the value with itself:
var i = 12.34;
console.log('i = ' + i);
console.log('i ⊕ i ⊕ i = ' + (i ^ i ^ i));
This will output:
i = 12.34
i ⊕ i ⊕ i = 12
I only added one plus(+) before string and that was solution!
+"052254" // 52254
Number()
Number(" 200.12 ") // Returns 200.12
Number("200.12") // Returns 200.12
Number("200") // Returns 200
parseInt()
parseInt(" 200.12 ") // Return 200
parseInt("200.12") // Return 200
parseInt("200") // Return 200
parseInt("Text information") // Returns NaN
parseFloat()
It will return the first number
parseFloat("200 400") // Returns 200
parseFloat("200") // Returns 200
parseFloat("Text information") // Returns NaN
parseFloat("200.10") // Return 200.10
Math.floor()
Round a number to the nearest integer
Math.floor(" 200.12 ") // Return 200
Math.floor("200.12") // Return 200
Math.floor("200") // Return 200
function doSth(){
var a = document.getElementById('input').value;
document.getElementById('number').innerHTML = toNumber(a) + 1;
}
function toNumber(str){
return +str;
}
<input id="input" type="text">
<input onclick="doSth()" type="submit">
<span id="number"></span>
This (probably) isn't the best solution for parsing an integer, but if you need to "extract" one, for example:
"1a2b3c" === 123
"198some text2hello world!30" === 198230
// ...
this would work (only for integers):
var str = '3a9b0c3d2e9f8g'
function extractInteger(str) {
var result = 0;
var factor = 1
for (var i = str.length; i > 0; i--) {
if (!isNaN(str[i - 1])) {
result += parseInt(str[i - 1]) * factor
factor *= 10
}
}
return result
}
console.log(extractInteger(str))
Of course, this would also work for parsing an integer, but would be slower than other methods.
You could also parse integers with this method and return NaN if the string isn't a number, but I don't see why you'd want to since this relies on parseInt internally and parseInt is probably faster.
var str = '3a9b0c3d2e9f8g'
function extractInteger(str) {
var result = 0;
var factor = 1
for (var i = str.length; i > 0; i--) {
if (isNaN(str[i - 1])) return NaN
result += parseInt(str[i - 1]) * factor
factor *= 10
}
return result
}
console.log(extractInteger(str))

The + operator in TypeScript [duplicate]

How do I convert a string to an integer in JavaScript?
The simplest way would be to use the native Number function:
var x = Number("1000")
If that doesn't work for you, then there are the parseInt, unary plus, parseFloat with floor, and Math.round methods.
parseInt()
var x = parseInt("1000", 10); // You want to use radix 10
// So you get a decimal number even with a leading 0 and an old browser ([IE8, Firefox 20, Chrome 22 and older][1])
Unary plus
If your string is already in the form of an integer:
var x = +"1000";
floor()
If your string is or might be a float and you want an integer:
var x = Math.floor("1000.01"); // floor() automatically converts string to number
Or, if you're going to be using Math.floor several times:
var floor = Math.floor;
var x = floor("1000.01");
parseFloat()
If you're the type who forgets to put the radix in when you call parseInt, you can use parseFloat and round it however you like. Here I use floor.
var floor = Math.floor;
var x = floor(parseFloat("1000.01"));
round()
Interestingly, Math.round (like Math.floor) will do a string to number conversion, so if you want the number rounded (or if you have an integer in the string), this is a great way, maybe my favorite:
var round = Math.round;
var x = round("1000"); // Equivalent to round("1000", 0)
Try parseInt function:
var number = parseInt("10");
But there is a problem. If you try to convert "010" using parseInt function, it detects as octal number, and will return number 8. So, you need to specify a radix (from 2 to 36). In this case base 10.
parseInt(string, radix)
Example:
var result = parseInt("010", 10) == 10; // Returns true
var result = parseInt("010") == 10; // Returns false
Note that parseInt ignores bad data after parsing anything valid.
This guid will parse as 51:
var result = parseInt('51e3daf6-b521-446a-9f5b-a1bb4d8bac36', 10) == 51; // Returns true
There are two main ways to convert a string to a number in JavaScript. One way is to parse it and the other way is to change its type to a Number. All of the tricks in the other answers (e.g., unary plus) involve implicitly coercing the type of the string to a number. You can also do the same thing explicitly with the Number function.
Parsing
var parsed = parseInt("97", 10);
parseInt and parseFloat are the two functions used for parsing strings to numbers. Parsing will stop silently if it hits a character it doesn't recognise, which can be useful for parsing strings like "92px", but it's also somewhat dangerous, since it won't give you any kind of error on bad input, instead you'll get back NaN unless the string starts with a number. Whitespace at the beginning of the string is ignored. Here's an example of it doing something different to what you want, and giving no indication that anything went wrong:
var widgetsSold = parseInt("97,800", 10); // widgetsSold is now 97
It's good practice to always specify the radix as the second argument. In older browsers, if the string started with a 0, it would be interpreted as octal if the radix wasn't specified which took a lot of people by surprise. The behaviour for hexadecimal is triggered by having the string start with 0x if no radix is specified, e.g., 0xff. The standard actually changed with ECMAScript 5, so modern browsers no longer trigger octal when there's a leading 0 if no radix has been specified. parseInt understands radixes up to base 36, in which case both upper and lower case letters are treated as equivalent.
Changing the Type of a String to a Number
All of the other tricks mentioned above that don't use parseInt, involve implicitly coercing the string into a number. I prefer to do this explicitly,
var cast = Number("97");
This has different behavior to the parse methods (although it still ignores whitespace). It's more strict: if it doesn't understand the whole of the string than it returns NaN, so you can't use it for strings like 97px. Since you want a primitive number rather than a Number wrapper object, make sure you don't put new in front of the Number function.
Obviously, converting to a Number gives you a value that might be a float rather than an integer, so if you want an integer, you need to modify it. There are a few ways of doing this:
var rounded = Math.floor(Number("97.654")); // other options are Math.ceil, Math.round
var fixed = Number("97.654").toFixed(0); // rounded rather than truncated
var bitwised = Number("97.654")|0; // do not use for large numbers
Any bitwise operator (here I've done a bitwise or, but you could also do double negation as in an earlier answer or a bit shift) will convert the value to a 32 bit integer, and most of them will convert to a signed integer. Note that this will not do want you want for large integers. If the integer cannot be represented in 32 bits, it will wrap.
~~"3000000000.654" === -1294967296
// This is the same as
Number("3000000000.654")|0
"3000000000.654" >>> 0 === 3000000000 // unsigned right shift gives you an extra bit
"300000000000.654" >>> 0 === 3647256576 // but still fails with larger numbers
To work correctly with larger numbers, you should use the rounding methods
Math.floor("3000000000.654") === 3000000000
// This is the same as
Math.floor(Number("3000000000.654"))
Bear in mind that coercion understands exponential notation and Infinity, so 2e2 is 200 rather than NaN, while the parse methods don't.
Custom
It's unlikely that either of these methods do exactly what you want. For example, usually I would want an error thrown if parsing fails, and I don't need support for Infinity, exponentials or leading whitespace. Depending on your use case, sometimes it makes sense to write a custom conversion function.
Always check that the output of Number or one of the parse methods is the sort of number you expect. You will almost certainly want to use isNaN to make sure the number is not NaN (usually the only way you find out that the parse failed).
ParseInt() and + are different
parseInt("10.3456") // returns 10
+"10.3456" // returns 10.3456
Fastest
var x = "1000"*1;
Test
Here is little comparison of speed (macOS only)... :)
For Chrome, 'plus' and 'mul' are fastest (>700,000,00 op/sec), 'Math.floor' is slowest. For Firefox, 'plus' is slowest (!) 'mul' is fastest (>900,000,000 op/sec). In Safari 'parseInt' is fastest, 'number' is slowest (but results are quite similar, >13,000,000 <31,000,000). So Safari for cast string to int is more than 10x slower than other browsers. So the winner is 'mul' :)
You can run it on your browser by this link
https://jsperf.com/js-cast-str-to-number/1
I also tested var x = ~~"1000";. On Chrome and Safari, it is a little bit slower than var x = "1000"*1 (<1%), and on Firefox it is a little bit faster (<1%).
I use this way of converting string to number:
var str = "25"; // String
var number = str*1; // Number
So, when multiplying by 1, the value does not change, but JavaScript automatically returns a number.
But as it is shown below, this should be used if you are sure that the str is a number (or can be represented as a number), otherwise it will return NaN - not a number.
You can create simple function to use, e.g.,
function toNumber(str) {
return str*1;
}
Try parseInt.
var number = parseInt("10", 10); //number will have value of 10.
I love this trick:
~~"2.123"; //2
~~"5"; //5
The double bitwise negative drops off anything after the decimal point AND converts it to a number format. I've been told it's slightly faster than calling functions and whatnot, but I'm not entirely convinced.
Another method I just saw here (a question about the JavaScript >>> operator, which is a zero-fill right shift) which shows that shifting a number by 0 with this operator converts the number to a uint32 which is nice if you also want it unsigned. Again, this converts to an unsigned integer, which can lead to strange behaviors if you use a signed number.
"-2.123" >>> 0; // 4294967294
"2.123" >>> 0; // 2
"-5" >>> 0; // 4294967291
"5" >>> 0; // 5
In JavaScript, you can do the following:
ParseInt
parseInt("10.5") // Returns 10
Multiplying with 1
var s = "10";
s = s*1; // Returns 10
Using the unary operator (+)
var s = "10";
s = +s; // Returns 10
Using a bitwise operator
(Note: It starts to break after 2140000000. Example: ~~"2150000000" = -2144967296)
var s = "10.5";
s = ~~s; // Returns 10
Using Math.floor() or Math.ceil()
var s = "10";
s = Math.floor(s) || Math.ceil(s); // Returns 10
Please see the below example. It will help answer your question.
Example Result
parseInt("4") 4
parseInt("5aaa") 5
parseInt("4.33333") 4
parseInt("aaa"); NaN (means "Not a Number")
By using parseint function, it will only give op of integer present and not the string.
Beware if you use parseInt to convert a float in scientific notation!
For example:
parseInt("5.6e-14")
will result in
5
instead of
0
Also as a side note: MooTools has the function toInt() which is used on any native string (or float (or integer)).
"2".toInt() // 2
"2px".toInt() // 2
2.toInt() // 2
We can use +(stringOfNumber) instead of using parseInt(stringOfNumber).
Example: +("21") returns int of 21, like the parseInt("21").
We can use this unary "+" operator for parsing float too...
To convert a String into Integer, I recommend using parseFloat and not parseInt. Here's why:
Using parseFloat:
parseFloat('2.34cms') //Output: 2.34
parseFloat('12.5') //Output: 12.5
parseFloat('012.3') //Output: 12.3
Using parseInt:
parseInt('2.34cms') //Output: 2
parseInt('12.5') //Output: 12
parseInt('012.3') //Output: 12
So if you have noticed parseInt discards the values after the decimals, whereas parseFloat lets you work with floating point numbers and hence more suitable if you want to retain the values after decimals. Use parseInt if and only if you are sure that you want the integer value.
There are many ways in JavaScript to convert a string to a number value... All are simple and handy. Choose the way which one works for you:
var num = Number("999.5"); //999.5
var num = parseInt("999.5", 10); //999
var num = parseFloat("999.5"); //999.5
var num = +"999.5"; //999.5
Also, any Math operation converts them to number, for example...
var num = "999.5" / 1; //999.5
var num = "999.5" * 1; //999.5
var num = "999.5" - 1 + 1; //999.5
var num = "999.5" - 0; //999.5
var num = Math.floor("999.5"); //999
var num = ~~"999.5"; //999
My prefer way is using + sign, which is the elegant way to convert a string to number in JavaScript.
Try str - 0 to convert string to number.
> str = '0'
> str - 0
0
> str = '123'
> str - 0
123
> str = '-12'
> str - 0
-12
> str = 'asdf'
> str - 0
NaN
> str = '12.34'
> str - 0
12.34
Here are two links to compare the performance of several ways to convert string to int
https://jsperf.com/number-vs-parseint-vs-plus
http://phrogz.net/js/string_to_number.html
Here is the easiest solution
let myNumber = "123" | 0;
More easy solution
let myNumber = +"123";
In my opinion, no answer covers all edge cases as parsing a float should result in an error.
function parseInteger(value) {
if(value === '') return NaN;
const number = Number(value);
return Number.isInteger(number) ? number : NaN;
}
parseInteger("4") // 4
parseInteger("5aaa") // NaN
parseInteger("4.33333") // NaN
parseInteger("aaa"); // NaN
The easiest way would be to use + like this
const strTen = "10"
const numTen = +strTen // string to number conversion
console.log(typeof strTen) // string
console.log(typeof numTen) // number
I actually needed to "save" a string as an integer, for a binding between C and JavaScript, so I convert the string into an integer value:
/*
Examples:
int2str( str2int("test") ) == "test" // true
int2str( str2int("t€st") ) // "t¬st", because "€".charCodeAt(0) is 8364, will be AND'ed with 0xff
Limitations:
maximum 4 characters, so it fits into an integer
*/
function str2int(the_str) {
var ret = 0;
var len = the_str.length;
if (len >= 1) ret += (the_str.charCodeAt(0) & 0xff) << 0;
if (len >= 2) ret += (the_str.charCodeAt(1) & 0xff) << 8;
if (len >= 3) ret += (the_str.charCodeAt(2) & 0xff) << 16;
if (len >= 4) ret += (the_str.charCodeAt(3) & 0xff) << 24;
return ret;
}
function int2str(the_int) {
var tmp = [
(the_int & 0x000000ff) >> 0,
(the_int & 0x0000ff00) >> 8,
(the_int & 0x00ff0000) >> 16,
(the_int & 0xff000000) >> 24
];
var ret = "";
for (var i=0; i<4; i++) {
if (tmp[i] == 0)
break;
ret += String.fromCharCode(tmp[i]);
}
return ret;
}
String to Number in JavaScript:
Unary + (most recommended)
+numStr is easy to use and has better performance compared with others
Supports both integers and decimals
console.log(+'123.45') // => 123.45
Some other options:
Parsing Strings:
parseInt(numStr) for integers
parseFloat(numStr) for both integers and decimals
console.log(parseInt('123.456')) // => 123
console.log(parseFloat('123')) // => 123
JavaScript Functions
Math functions like round(numStr), floor(numStr), ceil(numStr) for integers
Number(numStr) for both integers and decimals
console.log(Math.floor('123')) // => 123
console.log(Math.round('123.456')) // => 123
console.log(Math.ceil('123.454')) // => 124
console.log(Number('123.123')) // => 123.123
Unary Operators
All basic unary operators, +numStr, numStr-0, 1*numStr, numStr*1, and numStr/1
All support both integers and decimals
Be cautious about numStr+0. It returns a string.
console.log(+'123') // => 123
console.log('002'-0) // => 2
console.log(1*'5') // => 5
console.log('7.7'*1) // => 7.7
console.log(3.3/1) // =>3.3
console.log('123.123'+0, typeof ('123.123' + 0)) // => 123.1230 string
Bitwise Operators
Two tilde ~~numStr or left shift 0, numStr<<0
Supports only integers, but not decimals
console.log(~~'123') // => 123
console.log('0123'<<0) // => 123
console.log(~~'123.123') // => 123
console.log('123.123'<<0) // => 123
// Parsing
console.log(parseInt('123.456')) // => 123
console.log(parseFloat('123')) // => 123
// Function
console.log(Math.floor('123')) // => 123
console.log(Math.round('123.456')) // => 123
console.log(Math.ceil('123.454')) // => 124
console.log(Number('123.123')) // => 123.123
// Unary
console.log(+'123') // => 123
console.log('002'-0) // => 2
console.log(1*'5') // => 5
console.log('7.7'*1) // => 7.7
console.log(3.3/1) // => 3.3
console.log('123.123'+0, typeof ('123.123'+0)) // => 123.1230 string
// Bitwise
console.log(~~'123') // => 123
console.log('0123'<<0) // => 123
console.log(~~'123.123') // => 123
console.log('123.123'<<0) // => 123
function parseIntSmarter(str) {
// ParseInt is bad because it returns 22 for "22thisendsintext"
// Number() is returns NaN if it ends in non-numbers, but it returns 0 for empty or whitespace strings.
return isNaN(Number(str)) ? NaN : parseInt(str, 10);
}
You can use plus.
For example:
var personAge = '24';
var personAge1 = (+personAge)
then you can see the new variable's type bytypeof personAge1 ; which is number.
Summing the multiplication of digits with their respective power of ten:
i.e: 123 = 100+20+3 = 1100 + 2+10 + 31 = 1*(10^2) + 2*(10^1) + 3*(10^0)
function atoi(array) {
// Use exp as (length - i), other option would be
// to reverse the array.
// Multiply a[i] * 10^(exp) and sum
let sum = 0;
for (let i = 0; i < array.length; i++) {
let exp = array.length - (i+1);
let value = array[i] * Math.pow(10, exp);
sum += value;
}
return sum;
}
The safest way to ensure you get a valid integer:
let integer = (parseInt(value, 10) || 0);
Examples:
// Example 1 - Invalid value:
let value = null;
let integer = (parseInt(value, 10) || 0);
// => integer = 0
// Example 2 - Valid value:
let value = "1230.42";
let integer = (parseInt(value, 10) || 0);
// => integer = 1230
// Example 3 - Invalid value:
let value = () => { return 412 };
let integer = (parseInt(value, 10) || 0);
// => integer = 0
Another option is to double XOR the value with itself:
var i = 12.34;
console.log('i = ' + i);
console.log('i ⊕ i ⊕ i = ' + (i ^ i ^ i));
This will output:
i = 12.34
i ⊕ i ⊕ i = 12
I only added one plus(+) before string and that was solution!
+"052254" // 52254
Number()
Number(" 200.12 ") // Returns 200.12
Number("200.12") // Returns 200.12
Number("200") // Returns 200
parseInt()
parseInt(" 200.12 ") // Return 200
parseInt("200.12") // Return 200
parseInt("200") // Return 200
parseInt("Text information") // Returns NaN
parseFloat()
It will return the first number
parseFloat("200 400") // Returns 200
parseFloat("200") // Returns 200
parseFloat("Text information") // Returns NaN
parseFloat("200.10") // Return 200.10
Math.floor()
Round a number to the nearest integer
Math.floor(" 200.12 ") // Return 200
Math.floor("200.12") // Return 200
Math.floor("200") // Return 200
function doSth(){
var a = document.getElementById('input').value;
document.getElementById('number').innerHTML = toNumber(a) + 1;
}
function toNumber(str){
return +str;
}
<input id="input" type="text">
<input onclick="doSth()" type="submit">
<span id="number"></span>
This (probably) isn't the best solution for parsing an integer, but if you need to "extract" one, for example:
"1a2b3c" === 123
"198some text2hello world!30" === 198230
// ...
this would work (only for integers):
var str = '3a9b0c3d2e9f8g'
function extractInteger(str) {
var result = 0;
var factor = 1
for (var i = str.length; i > 0; i--) {
if (!isNaN(str[i - 1])) {
result += parseInt(str[i - 1]) * factor
factor *= 10
}
}
return result
}
console.log(extractInteger(str))
Of course, this would also work for parsing an integer, but would be slower than other methods.
You could also parse integers with this method and return NaN if the string isn't a number, but I don't see why you'd want to since this relies on parseInt internally and parseInt is probably faster.
var str = '3a9b0c3d2e9f8g'
function extractInteger(str) {
var result = 0;
var factor = 1
for (var i = str.length; i > 0; i--) {
if (isNaN(str[i - 1])) return NaN
result += parseInt(str[i - 1]) * factor
factor *= 10
}
return result
}
console.log(extractInteger(str))

ES6 +new Javascript Syntax [duplicate]

I'm trying to understand unary operators in javascript, I found this guide here http://wiki.answers.com/Q/What_are_unary_operators_in_javascript most of it makes sense but what I don't understand is how the following examples would be used in an actual code example:
+a;
-a;
To my understanding the +a; is meant to make the variable the positive value of a and the -a; is meant to make the variable the negative value of a. I've tried a number of examples like:
a = -10;
a = +a;
document.writeln(a);
And the output is still -10;
I've also tried:
a = false;
a = +a;
document.writeln(a);
And the output is 0;
What is a practical code example of these unary operators?
The + operator doesn't change the sign of the value, and the - operator does change the sign. The outcome of both operators depend on the sign of the original value, neither operator makes the value positive or negative regardless of the original sign.
var a = 4;
a = -a; // -4
a = +a; // -4
The abs function does what you think that the + opreator does; it makes the value positive regardless of the original sign.
var a =-4;
a = Math.abs(a); // 4
Doing +a is practically the same as doing a * 1; it converts the value in a to a number if needed, but after that it doesn't change the value.
var a = "5";
a = +a; // 5
The + operator is used sometimes to convert string to numbers, but you have the parseInt and parseFloat functions for doing the conversion in a more specific way.
var a = "5";
a = parseInt(a, 10); //5
One example is that they can be used to convert a string to a number,
var threeStr = '3.0'
var three = +threeStr
console.log(threeStr + 3) // '3.03'
console.log(three + 3) //6
I would like to explain this from basic mathematical point:
The multiplying rules:
Positive x Positive = Positive: 3 x 2 = 6
Negative x Negative = Positive: (-2) x (-8) = 16
Negative x Positive = Negative: (-3) x 4 = -12
Positive x Negative = Negative: 3 x (-4) = -12
Considering you example:
a = -10;
a = +a
document.writeln(a);
+a = +(-10) = Positive x Negative = Negative = -10
a = false;
a = +a;
document.writeln(a);
false == 0, +a = +(+0) = Positive * Positive = Positive = 0 (maybe use true is a better example)
a = 1
b = -a
console.log(b)
output
-1
'+' operator in a variable 'a' simply means : a
'-' operator in a variable 'a' simply means : -a
Since, in above example
a=-10;
a= +a; // means a, ie, +(-10) which is -10
but,
a= -a; // means -a, ie, -(-10) which is +10
+a means a*1
and
-a means a*(-1)
Thats it!!!!!!
Try this
false == 0 // returns true
So,
a = false
a = +a //a * 1
console.log(a) // prints 0 as expected

replacing string number with actual number itself [duplicate]

How do I convert a string to an integer in JavaScript?
The simplest way would be to use the native Number function:
var x = Number("1000")
If that doesn't work for you, then there are the parseInt, unary plus, parseFloat with floor, and Math.round methods.
parseInt()
var x = parseInt("1000", 10); // You want to use radix 10
// So you get a decimal number even with a leading 0 and an old browser ([IE8, Firefox 20, Chrome 22 and older][1])
Unary plus
If your string is already in the form of an integer:
var x = +"1000";
floor()
If your string is or might be a float and you want an integer:
var x = Math.floor("1000.01"); // floor() automatically converts string to number
Or, if you're going to be using Math.floor several times:
var floor = Math.floor;
var x = floor("1000.01");
parseFloat()
If you're the type who forgets to put the radix in when you call parseInt, you can use parseFloat and round it however you like. Here I use floor.
var floor = Math.floor;
var x = floor(parseFloat("1000.01"));
round()
Interestingly, Math.round (like Math.floor) will do a string to number conversion, so if you want the number rounded (or if you have an integer in the string), this is a great way, maybe my favorite:
var round = Math.round;
var x = round("1000"); // Equivalent to round("1000", 0)
Try parseInt function:
var number = parseInt("10");
But there is a problem. If you try to convert "010" using parseInt function, it detects as octal number, and will return number 8. So, you need to specify a radix (from 2 to 36). In this case base 10.
parseInt(string, radix)
Example:
var result = parseInt("010", 10) == 10; // Returns true
var result = parseInt("010") == 10; // Returns false
Note that parseInt ignores bad data after parsing anything valid.
This guid will parse as 51:
var result = parseInt('51e3daf6-b521-446a-9f5b-a1bb4d8bac36', 10) == 51; // Returns true
There are two main ways to convert a string to a number in JavaScript. One way is to parse it and the other way is to change its type to a Number. All of the tricks in the other answers (e.g., unary plus) involve implicitly coercing the type of the string to a number. You can also do the same thing explicitly with the Number function.
Parsing
var parsed = parseInt("97", 10);
parseInt and parseFloat are the two functions used for parsing strings to numbers. Parsing will stop silently if it hits a character it doesn't recognise, which can be useful for parsing strings like "92px", but it's also somewhat dangerous, since it won't give you any kind of error on bad input, instead you'll get back NaN unless the string starts with a number. Whitespace at the beginning of the string is ignored. Here's an example of it doing something different to what you want, and giving no indication that anything went wrong:
var widgetsSold = parseInt("97,800", 10); // widgetsSold is now 97
It's good practice to always specify the radix as the second argument. In older browsers, if the string started with a 0, it would be interpreted as octal if the radix wasn't specified which took a lot of people by surprise. The behaviour for hexadecimal is triggered by having the string start with 0x if no radix is specified, e.g., 0xff. The standard actually changed with ECMAScript 5, so modern browsers no longer trigger octal when there's a leading 0 if no radix has been specified. parseInt understands radixes up to base 36, in which case both upper and lower case letters are treated as equivalent.
Changing the Type of a String to a Number
All of the other tricks mentioned above that don't use parseInt, involve implicitly coercing the string into a number. I prefer to do this explicitly,
var cast = Number("97");
This has different behavior to the parse methods (although it still ignores whitespace). It's more strict: if it doesn't understand the whole of the string than it returns NaN, so you can't use it for strings like 97px. Since you want a primitive number rather than a Number wrapper object, make sure you don't put new in front of the Number function.
Obviously, converting to a Number gives you a value that might be a float rather than an integer, so if you want an integer, you need to modify it. There are a few ways of doing this:
var rounded = Math.floor(Number("97.654")); // other options are Math.ceil, Math.round
var fixed = Number("97.654").toFixed(0); // rounded rather than truncated
var bitwised = Number("97.654")|0; // do not use for large numbers
Any bitwise operator (here I've done a bitwise or, but you could also do double negation as in an earlier answer or a bit shift) will convert the value to a 32 bit integer, and most of them will convert to a signed integer. Note that this will not do want you want for large integers. If the integer cannot be represented in 32 bits, it will wrap.
~~"3000000000.654" === -1294967296
// This is the same as
Number("3000000000.654")|0
"3000000000.654" >>> 0 === 3000000000 // unsigned right shift gives you an extra bit
"300000000000.654" >>> 0 === 3647256576 // but still fails with larger numbers
To work correctly with larger numbers, you should use the rounding methods
Math.floor("3000000000.654") === 3000000000
// This is the same as
Math.floor(Number("3000000000.654"))
Bear in mind that coercion understands exponential notation and Infinity, so 2e2 is 200 rather than NaN, while the parse methods don't.
Custom
It's unlikely that either of these methods do exactly what you want. For example, usually I would want an error thrown if parsing fails, and I don't need support for Infinity, exponentials or leading whitespace. Depending on your use case, sometimes it makes sense to write a custom conversion function.
Always check that the output of Number or one of the parse methods is the sort of number you expect. You will almost certainly want to use isNaN to make sure the number is not NaN (usually the only way you find out that the parse failed).
ParseInt() and + are different
parseInt("10.3456") // returns 10
+"10.3456" // returns 10.3456
Fastest
var x = "1000"*1;
Test
Here is little comparison of speed (macOS only)... :)
For Chrome, 'plus' and 'mul' are fastest (>700,000,00 op/sec), 'Math.floor' is slowest. For Firefox, 'plus' is slowest (!) 'mul' is fastest (>900,000,000 op/sec). In Safari 'parseInt' is fastest, 'number' is slowest (but results are quite similar, >13,000,000 <31,000,000). So Safari for cast string to int is more than 10x slower than other browsers. So the winner is 'mul' :)
You can run it on your browser by this link
https://jsperf.com/js-cast-str-to-number/1
I also tested var x = ~~"1000";. On Chrome and Safari, it is a little bit slower than var x = "1000"*1 (<1%), and on Firefox it is a little bit faster (<1%).
I use this way of converting string to number:
var str = "25"; // String
var number = str*1; // Number
So, when multiplying by 1, the value does not change, but JavaScript automatically returns a number.
But as it is shown below, this should be used if you are sure that the str is a number (or can be represented as a number), otherwise it will return NaN - not a number.
You can create simple function to use, e.g.,
function toNumber(str) {
return str*1;
}
Try parseInt.
var number = parseInt("10", 10); //number will have value of 10.
I love this trick:
~~"2.123"; //2
~~"5"; //5
The double bitwise negative drops off anything after the decimal point AND converts it to a number format. I've been told it's slightly faster than calling functions and whatnot, but I'm not entirely convinced.
Another method I just saw here (a question about the JavaScript >>> operator, which is a zero-fill right shift) which shows that shifting a number by 0 with this operator converts the number to a uint32 which is nice if you also want it unsigned. Again, this converts to an unsigned integer, which can lead to strange behaviors if you use a signed number.
"-2.123" >>> 0; // 4294967294
"2.123" >>> 0; // 2
"-5" >>> 0; // 4294967291
"5" >>> 0; // 5
In JavaScript, you can do the following:
ParseInt
parseInt("10.5") // Returns 10
Multiplying with 1
var s = "10";
s = s*1; // Returns 10
Using the unary operator (+)
var s = "10";
s = +s; // Returns 10
Using a bitwise operator
(Note: It starts to break after 2140000000. Example: ~~"2150000000" = -2144967296)
var s = "10.5";
s = ~~s; // Returns 10
Using Math.floor() or Math.ceil()
var s = "10";
s = Math.floor(s) || Math.ceil(s); // Returns 10
Please see the below example. It will help answer your question.
Example Result
parseInt("4") 4
parseInt("5aaa") 5
parseInt("4.33333") 4
parseInt("aaa"); NaN (means "Not a Number")
By using parseint function, it will only give op of integer present and not the string.
Beware if you use parseInt to convert a float in scientific notation!
For example:
parseInt("5.6e-14")
will result in
5
instead of
0
Also as a side note: MooTools has the function toInt() which is used on any native string (or float (or integer)).
"2".toInt() // 2
"2px".toInt() // 2
2.toInt() // 2
We can use +(stringOfNumber) instead of using parseInt(stringOfNumber).
Example: +("21") returns int of 21, like the parseInt("21").
We can use this unary "+" operator for parsing float too...
To convert a String into Integer, I recommend using parseFloat and not parseInt. Here's why:
Using parseFloat:
parseFloat('2.34cms') //Output: 2.34
parseFloat('12.5') //Output: 12.5
parseFloat('012.3') //Output: 12.3
Using parseInt:
parseInt('2.34cms') //Output: 2
parseInt('12.5') //Output: 12
parseInt('012.3') //Output: 12
So if you have noticed parseInt discards the values after the decimals, whereas parseFloat lets you work with floating point numbers and hence more suitable if you want to retain the values after decimals. Use parseInt if and only if you are sure that you want the integer value.
There are many ways in JavaScript to convert a string to a number value... All are simple and handy. Choose the way which one works for you:
var num = Number("999.5"); //999.5
var num = parseInt("999.5", 10); //999
var num = parseFloat("999.5"); //999.5
var num = +"999.5"; //999.5
Also, any Math operation converts them to number, for example...
var num = "999.5" / 1; //999.5
var num = "999.5" * 1; //999.5
var num = "999.5" - 1 + 1; //999.5
var num = "999.5" - 0; //999.5
var num = Math.floor("999.5"); //999
var num = ~~"999.5"; //999
My prefer way is using + sign, which is the elegant way to convert a string to number in JavaScript.
Try str - 0 to convert string to number.
> str = '0'
> str - 0
0
> str = '123'
> str - 0
123
> str = '-12'
> str - 0
-12
> str = 'asdf'
> str - 0
NaN
> str = '12.34'
> str - 0
12.34
Here are two links to compare the performance of several ways to convert string to int
https://jsperf.com/number-vs-parseint-vs-plus
http://phrogz.net/js/string_to_number.html
Here is the easiest solution
let myNumber = "123" | 0;
More easy solution
let myNumber = +"123";
In my opinion, no answer covers all edge cases as parsing a float should result in an error.
function parseInteger(value) {
if(value === '') return NaN;
const number = Number(value);
return Number.isInteger(number) ? number : NaN;
}
parseInteger("4") // 4
parseInteger("5aaa") // NaN
parseInteger("4.33333") // NaN
parseInteger("aaa"); // NaN
The easiest way would be to use + like this
const strTen = "10"
const numTen = +strTen // string to number conversion
console.log(typeof strTen) // string
console.log(typeof numTen) // number
I actually needed to "save" a string as an integer, for a binding between C and JavaScript, so I convert the string into an integer value:
/*
Examples:
int2str( str2int("test") ) == "test" // true
int2str( str2int("t€st") ) // "t¬st", because "€".charCodeAt(0) is 8364, will be AND'ed with 0xff
Limitations:
maximum 4 characters, so it fits into an integer
*/
function str2int(the_str) {
var ret = 0;
var len = the_str.length;
if (len >= 1) ret += (the_str.charCodeAt(0) & 0xff) << 0;
if (len >= 2) ret += (the_str.charCodeAt(1) & 0xff) << 8;
if (len >= 3) ret += (the_str.charCodeAt(2) & 0xff) << 16;
if (len >= 4) ret += (the_str.charCodeAt(3) & 0xff) << 24;
return ret;
}
function int2str(the_int) {
var tmp = [
(the_int & 0x000000ff) >> 0,
(the_int & 0x0000ff00) >> 8,
(the_int & 0x00ff0000) >> 16,
(the_int & 0xff000000) >> 24
];
var ret = "";
for (var i=0; i<4; i++) {
if (tmp[i] == 0)
break;
ret += String.fromCharCode(tmp[i]);
}
return ret;
}
String to Number in JavaScript:
Unary + (most recommended)
+numStr is easy to use and has better performance compared with others
Supports both integers and decimals
console.log(+'123.45') // => 123.45
Some other options:
Parsing Strings:
parseInt(numStr) for integers
parseFloat(numStr) for both integers and decimals
console.log(parseInt('123.456')) // => 123
console.log(parseFloat('123')) // => 123
JavaScript Functions
Math functions like round(numStr), floor(numStr), ceil(numStr) for integers
Number(numStr) for both integers and decimals
console.log(Math.floor('123')) // => 123
console.log(Math.round('123.456')) // => 123
console.log(Math.ceil('123.454')) // => 124
console.log(Number('123.123')) // => 123.123
Unary Operators
All basic unary operators, +numStr, numStr-0, 1*numStr, numStr*1, and numStr/1
All support both integers and decimals
Be cautious about numStr+0. It returns a string.
console.log(+'123') // => 123
console.log('002'-0) // => 2
console.log(1*'5') // => 5
console.log('7.7'*1) // => 7.7
console.log(3.3/1) // =>3.3
console.log('123.123'+0, typeof ('123.123' + 0)) // => 123.1230 string
Bitwise Operators
Two tilde ~~numStr or left shift 0, numStr<<0
Supports only integers, but not decimals
console.log(~~'123') // => 123
console.log('0123'<<0) // => 123
console.log(~~'123.123') // => 123
console.log('123.123'<<0) // => 123
// Parsing
console.log(parseInt('123.456')) // => 123
console.log(parseFloat('123')) // => 123
// Function
console.log(Math.floor('123')) // => 123
console.log(Math.round('123.456')) // => 123
console.log(Math.ceil('123.454')) // => 124
console.log(Number('123.123')) // => 123.123
// Unary
console.log(+'123') // => 123
console.log('002'-0) // => 2
console.log(1*'5') // => 5
console.log('7.7'*1) // => 7.7
console.log(3.3/1) // => 3.3
console.log('123.123'+0, typeof ('123.123'+0)) // => 123.1230 string
// Bitwise
console.log(~~'123') // => 123
console.log('0123'<<0) // => 123
console.log(~~'123.123') // => 123
console.log('123.123'<<0) // => 123
function parseIntSmarter(str) {
// ParseInt is bad because it returns 22 for "22thisendsintext"
// Number() is returns NaN if it ends in non-numbers, but it returns 0 for empty or whitespace strings.
return isNaN(Number(str)) ? NaN : parseInt(str, 10);
}
You can use plus.
For example:
var personAge = '24';
var personAge1 = (+personAge)
then you can see the new variable's type bytypeof personAge1 ; which is number.
Summing the multiplication of digits with their respective power of ten:
i.e: 123 = 100+20+3 = 1100 + 2+10 + 31 = 1*(10^2) + 2*(10^1) + 3*(10^0)
function atoi(array) {
// Use exp as (length - i), other option would be
// to reverse the array.
// Multiply a[i] * 10^(exp) and sum
let sum = 0;
for (let i = 0; i < array.length; i++) {
let exp = array.length - (i+1);
let value = array[i] * Math.pow(10, exp);
sum += value;
}
return sum;
}
The safest way to ensure you get a valid integer:
let integer = (parseInt(value, 10) || 0);
Examples:
// Example 1 - Invalid value:
let value = null;
let integer = (parseInt(value, 10) || 0);
// => integer = 0
// Example 2 - Valid value:
let value = "1230.42";
let integer = (parseInt(value, 10) || 0);
// => integer = 1230
// Example 3 - Invalid value:
let value = () => { return 412 };
let integer = (parseInt(value, 10) || 0);
// => integer = 0
Another option is to double XOR the value with itself:
var i = 12.34;
console.log('i = ' + i);
console.log('i ⊕ i ⊕ i = ' + (i ^ i ^ i));
This will output:
i = 12.34
i ⊕ i ⊕ i = 12
I only added one plus(+) before string and that was solution!
+"052254" // 52254
Number()
Number(" 200.12 ") // Returns 200.12
Number("200.12") // Returns 200.12
Number("200") // Returns 200
parseInt()
parseInt(" 200.12 ") // Return 200
parseInt("200.12") // Return 200
parseInt("200") // Return 200
parseInt("Text information") // Returns NaN
parseFloat()
It will return the first number
parseFloat("200 400") // Returns 200
parseFloat("200") // Returns 200
parseFloat("Text information") // Returns NaN
parseFloat("200.10") // Return 200.10
Math.floor()
Round a number to the nearest integer
Math.floor(" 200.12 ") // Return 200
Math.floor("200.12") // Return 200
Math.floor("200") // Return 200
function doSth(){
var a = document.getElementById('input').value;
document.getElementById('number').innerHTML = toNumber(a) + 1;
}
function toNumber(str){
return +str;
}
<input id="input" type="text">
<input onclick="doSth()" type="submit">
<span id="number"></span>
This (probably) isn't the best solution for parsing an integer, but if you need to "extract" one, for example:
"1a2b3c" === 123
"198some text2hello world!30" === 198230
// ...
this would work (only for integers):
var str = '3a9b0c3d2e9f8g'
function extractInteger(str) {
var result = 0;
var factor = 1
for (var i = str.length; i > 0; i--) {
if (!isNaN(str[i - 1])) {
result += parseInt(str[i - 1]) * factor
factor *= 10
}
}
return result
}
console.log(extractInteger(str))
Of course, this would also work for parsing an integer, but would be slower than other methods.
You could also parse integers with this method and return NaN if the string isn't a number, but I don't see why you'd want to since this relies on parseInt internally and parseInt is probably faster.
var str = '3a9b0c3d2e9f8g'
function extractInteger(str) {
var result = 0;
var factor = 1
for (var i = str.length; i > 0; i--) {
if (isNaN(str[i - 1])) return NaN
result += parseInt(str[i - 1]) * factor
factor *= 10
}
return result
}
console.log(extractInteger(str))

parseInt vs unary plus, when to use which?

What are the differences between this line:
var a = parseInt("1", 10); // a === 1
and this line
var a = +"1"; // a === 1
This jsperf test shows that the unary operator is much faster in the current chrome version, assuming it is for node.js!?
If I try to convert strings which are not numbers both return NaN:
var b = parseInt("test", 10); // b === NaN
var b = +"test"; // b === NaN
So when should I prefer using parseInt over the unary plus (especially in node.js)???
edit: and what's the difference to the double tilde operator ~~?
The ultimate whatever-to-number conversion table:
EXPRS = [
'parseInt(x)',
'parseFloat(x)',
'Number(x)',
'+x',
'~~x',
'x>>>0',
'isNaN(x)'
];
VALUES = [
'"123"',
'"+123"',
'"-123"',
'"123.45"',
'"-123.45"',
'"12e5"',
'"12e-5"',
'"0123"',
'"0000123"',
'"0b111"',
'"0o10"',
'"0xBABE"',
'"4294967295"',
'"123456789012345678"',
'"12e999"',
'""',
'"123foo"',
'"123.45foo"',
'" 123 "',
'"foo"',
'"12e"',
'"0b567"',
'"0o999"',
'"0xFUZZ"',
'"+0"',
'"-0"',
'"Infinity"',
'"+Infinity"',
'"-Infinity"',
'BigInt(1)',
'null',
'undefined',
'true',
'false',
'Infinity',
'NaN',
'{}',
'{valueOf: function(){return 42}}',
'{toString: function(){return "56"}}',
];
//////
function wrap(tag, s) {
if (s && s.join)
s = s.join('');
return '<' + tag + '>' + String(s) + '</' + tag + '>';
}
function table(head, rows) {
return wrap('table', [
wrap('thead', tr(head)),
wrap('tbody', rows.map(tr))
]);
}
function tr(row) {
return wrap('tr', row.map(function (s) {
return wrap('td', s)
}));
}
function val(n) {
return n === true || Number.isNaN(n) || n === "Error" ? wrap('b', n) : String(n);
}
var rows = VALUES.map(function (v) {
var x = eval('(' + v + ')');
return [v].concat(EXPRS.map(function (e) {
try {
return val(eval(e));
} catch {
return val("Error");
}
}));
});
document.body.innerHTML = table(["x"].concat(EXPRS), rows);
table { border-collapse: collapse }
tr:nth-child(odd) { background: #fafafa }
td { border: 1px solid #e0e0e0; padding: 5px; font: 12px monospace }
td:not(:first-child) { text-align: right }
thead td { background: #3663AE; color: white }
b { color: red }
Well, here are a few differences I know of:
An empty string "" evaluates to a 0, while parseInt evaluates it to NaN. IMO, a blank string should be a NaN.
+'' === 0; //true
isNaN(parseInt('',10)); //true
The unary + acts more like parseFloat since it also accepts decimals.
parseInt on the other hand stops parsing when it sees a non-numerical character, like the period that is intended to be a decimal point ..
+'2.3' === 2.3; //true
parseInt('2.3',10) === 2; //true
parseInt and parseFloat parses and builds the string left to right. If they see an invalid character, it returns what has been parsed (if any) as a number, and NaN if none was parsed as a number.
The unary + on the other hand will return NaN if the entire string is non-convertible to a number.
parseInt('2a',10) === 2; //true
parseFloat('2a') === 2; //true
isNaN(+'2a'); //true
As seen in the comment of #Alex K., parseInt and parseFloat will parse by character. This means hex and exponent notations will fail since the x and e are treated as non-numerical components (at least on base10).
The unary + will convert them properly though.
parseInt('2e3',10) === 2; //true. This is supposed to be 2000
+'2e3' === 2000; //true. This one's correct.
parseInt("0xf", 10) === 0; //true. This is supposed to be 15
+'0xf' === 15; //true. This one's correct.
The table in thg435's answer I believe is comprehensive, however we can summarize with the following patterns:
Unary plus does not treat all falsy values the same, but they all come out falsy.
Unary plus sends true to 1, but "true" to NaN.
On the other hand, parseInt is more liberal for strings that are not pure digits. parseInt('123abc') === 123, whereas + reports NaN.
Number will accept valid decimal numbers, whereas parseInt merely drops everything past the decimal. Thus parseInt mimics C behavior, but is perhaps not ideal for evaluating user input.
Both trim whitespace in strings.
parseInt, being a badly designed parser, accepts octal and hexadecimal input. Unary plus only takes hexademical.
Falsy values convert to Number following what would make sense in C: null and false are both zero. "" going to 0 doesn't quite follow this convention but makes enough sense to me.
Therefore I think if you are validating user input, unary plus has correct behavior for everything except it accepts decimals (but in my real life cases I'm more interested in catching email input instead of userId, value omitted entirely, etc.), whereas parseInt is too liberal.
Be carefull, parseInt is faster than + unary operator in Node.JS,
it's false that + or |0 are faster, them are faster only for NaN elements.
Check this out:
var arg=process.argv[2];
rpt=20000;
mrc=1000;
a=[];
b=1024*1024*1024*1024;
for (var i=0;i<rpt;i++)
a[i]=Math.floor(Math.random()*b)+' ';
t0=Date.now();
if ((arg==1)||(arg===undefined))
for (var j=0;j<mrc;j++) for (var i=0;i<rpt;i++) {
c=a[i]-0;
}
t1=Date.now();
if ((arg==2)||(arg===undefined)) {
for (var j=0;j<mrc;j++) for (var i=0;i<rpt;i++) {
d=a[i]|0;
}
}
t2=Date.now();
if ((arg==3)||(arg===undefined)) {
for (var j=0;j<mrc;j++) for (var i=0;i<rpt;i++) {
e=parseInt(a[i]);
}
}
t3=Date.now();
if ((arg==3)||(arg===undefined)) {
for (var j=0;j<mrc;j++) for (var i=0;i<rpt;i++) {
f=+a[i];
}
}
t4=Date.now();
console.log(a[i-1],c,d,e,f);
console.log('Eseguiti: '+rpt*mrc+' cicli');
console.log('parseInt '+(t3-t2));
console.log('|0 '+(t2-t1));
console.log('-0 '+(t1-t0));
console.log('+ '+(t4-t3));
I recommend use Math.floor (or ~~ if you know numbers are positive) instead of parseString. +(expression) is out of scope, because +(expression) is more like parseFloat. Look this little benchmark:
// 1000000 iterations each one
node test_speed
Testing ~~, time: 5 ms
Testing parseInt with number, time: 25 ms
Testing parseInt with string, time: 386 ms
Testing Math.floor, time: 18 ms
The source code of benchmark:
/* el propósito de este script es evaluar
que expresiones se ejecutan más rápido para así
decidir cuál usar */
main()
async function main(){
let time, x
let number = 23456.23457
let test1 = ()=>{
x = 0
time = Date.now()
for(let i=0;i<1000000;i++){
let op = Math.floor(number / 3600)
x = op
}
console.info("Testing Math.floor, time:", Date.now() - time, "ms")
}
let test2 = ()=>{
x = 0
time = Date.now()
for(let i=0;i<1000000;i++){
let op = parseInt(number / 3600)
x = op
}
console.info("Testing parseInt with number, time:", Date.now() - time, "ms")
}
let test3 = ()=>{
x = 0
time = Date.now()
for(let i=0;i<1000000;i++){
let op = parseInt((number / 3600).toString())
x = op
}
console.info("Testing parseInt with string, time:", Date.now() - time, "ms")
}
let test4 = ()=>{
x = 0
time = Date.now()
for(let i=0;i<1000000;i++){
let op = ~~(number / 3600)
x = op
}
console.info("Testing ~~, time:", Date.now() - time, "ms")
}
test4()
test2()
test3()
test1()
}
Consider performance too. I was suprised that parseInt beats unary plus on iOS :) This is helpful for web apps with heavy CPU consumption only. As a rule-of-thumb I'd suggest JS opt-guys to consider any JS operator over another one from the mobile performance point of view nowadays.
So, go mobile-first ;)

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