I have a simple question to ask, in which I am slightly embarrassed to ask, but I realize that I won't learn unless I ask.
When looking at reversing a string, I recognize that reversing a string requires you to split up the string, reverse it, and then re-join it. Like so.
var stringReverse = function (n){
return n.split("").reverse().join("");
}
console.log(stringReverse("hello"));
However, I was trying to reverse a number, much of the principles were very similar except for one part. The code below is:
var reverse_a_number = function (n){
n = n + "";
return n.split("").reverse().join("");
}
console.log(reverse_a_number(32243));
My question is why am I needed to bring in the " n = n + " ";" to the code? I was assuming that the same principles would be similar regardless of it being a string, or an integer.
Much thanks in advance, and I apologize that this question is elementary.
why am I needed to bring in the " n = n + " ";" to the code?
Adding + "" will make a cast to String, this way you can use String functions (.split).
The integer have only functionality of a Number. If you want to treat the Number as a String you need to cast it (+ "") or convert it (.toString())
The .reverse() function come from Array object that is created when you use String function .split().
With .join() you come back to String from Array (of characters).
If you want to come back to Number after reverting, you can choose one of these functions.
To put it simply, the docs require it to be a string. You could combine your two methods by doing exactly what you're doing in reverse_a_number (it works for both). Also, don't be embarrassed to ask questions, it's how you learn :)
Number doesn't have reverse and split method directly and you should convert number to string that be able reverse it.
to convert it you can add an empty string after it, like you.
just it.
Javascript sets the type of a variable at runtime.
If she (yes, it's a girl) sees that you only have ciphers, she will consider it's an integer.
Adding + ""; casts it into a string, which is an array of chars.
Your string is stored a lil bit like : ['h', 'e', 'l', 'l', 'o']
an integer is stored as {0011001010101...}
Explanation
You are passing in a number, not a string. When you combine a number with a string ("") it assumes you want to make a string. So you are really converting it to a string. To an array, then back to a string. If you attempt to split a number, the compiler will throw an error. More exactly
TypeError: undefined is not a function (evaluating 'n.split('')')
So what you really are doing is making the number into a String. There are different methods you can use, take a look here.
n += '';(String) ->
.split() (Array) -> .split() (Array) -> .join() (String)
Your function is actually producing and returning a string
Alternative Function
I'm going to critique ;) , you could shorten, and improve this function using the following.
var reverse_a_number = function (n){
return +(n += "").split("").reverse().join("");
}
What does this do?
n = n + '' has a special operator, +=. We can shorten this to on-line by using this inside parenthesis. The + will convert it into a Integer
A number doesn't have the split method. You have to convert it into a string, which does have split.
You can use typeof to find out the type of a variable. The following code snippet demonstrates the types of a number and a string, and shows the value of the split attribute for each one. Note that split is undefined for the number.
var n = 42;
document.write(typeof n, '<br />', n.split, '<br />', '<br />');
var s = ''+n;
document.write(typeof s, '<br />', s.split);
If you want to reverse an integer by treating it as an integer, without using string operations, you can do the following.
function reverseInteger(n) {
var result = 0;
while (n != 0) {
var digit = n%10;
result = 10*result + digit;
n = (n-digit)/10;
}
return result;
}
var n = 3141590123456;
document.write(n, '<br />');
document.write(reverseInteger(n));
Note that the last digit of n is n%10. If we subtract the last digit and divide n by ten, the effect is to shift n one digit to the right. We keep doing this and build up result in reverse by multiplying it by ten on each iteration and adding the digit that we just removed from n.
Related
This question already has answers here:
JavaScript: How to reverse a number?
(19 answers)
Closed 3 years ago.
Result shows "n.split is not a function" unless i include n=n+" " the following code.What does third line mean?
function reverse_a_number(n)
{
n = n + "";
return n.split("").reverse().join("");
}
console.log(reverse_a_number(32243));
There is no split function in Number.prototype. So, n = n + "" is just a simple way to convert a number to a string.
From the spec
If Type(lprim) is String or Type(rprim) is String, then
Return the String that is the result of concatenating ToString(lprim) followed by ToString(rprim)
If one of the operands in an expression with + is a string, the other operand is also coerced to a string and concatenated with it
console.log( 1 + 1 ) // sum
console.log( 1 + "1" ) // concatenation
console.log( true + "string" ) // concatenation
In javascript , there is no Explicit declaration of datatype, by assigning value to the variable , it implicitly takes the datatype like int,string.
In your case,Simple you are applying String function to integer , so you are getting Error.
So first convert integer value into String by using "toString()" function.
Solution:
function reverse_a_number(n) {
//Casting
n=n.toString();
return Number(n.split("").reverse().join(""));
}
console.log(reverse_a_number(32243));
There is no split function for Number. You can do this as an alternate
+String.prototype.split.call(32243,'').reverse().join('')
What the above code does?
I am using split method in String class via context switching for number which returns array.
Then we are reversing the number and joining it.
Then unary plus converts it to number.
As #briosheje mentioned, you can also use the following
+[...''+32243].reverse().join('')
Cast the number to a string and then use split as numerical values don't have the split function. Again cast it to a number while returning
function reverse_a_number(n) {
n=n.toString();
return Number(n.split("").reverse().join(""));
}
console.log(reverse_a_number(32243));
The reason is that split method works only on string values and your passing integer value as argument, that's why it's working only after casting it to string
You can't split a number. By using n = n + "", you're casting it a string and then splitting it. However, you're also returning a string! You'll want to cast it back to an integer before you return it.
Hmm.. I think this could be solved easily.
turn the number to a string, this lets you turn it to an array
Split it to a array
use array's function 'reversed'
join it
turn it to an number or int again.
const number = 3211232;
const numberReversed = parseInt(number.toString().split("").reverse().join(""));
console.log(numberReversed);
I am a beginner to coding and JavaScript but I am doing a practice exercise and I came across something I am unsure about.
var nameLength = parseInt(fullName.length);
var nameLength = fullName.length;
I used the first line not even thinking it would already be an integer, so should I still have included the parseInt or not?
Yes, remove var nameLength = parseInt(fullName.length); Below is your explanation:The parseInt() method in JavaScript is used to turn the integer value of a string into an integer. If I have string, say var s = "3";, I could use the + operator to it, but it wouldn't add as if they were numbers (ex. s += 9;, then s would equal "39"). You call the parseInt() method only if you have a value with the type of string. In your case, and in most, if not all languages, the .length or .length() of anything will return an integer. What you're doing is trying to convert a number to a number, which is (after I googled the definition) extraneous.
What I'm trying to do is to make a progress bar for donation. My html structure is:
<div class="hgoal" style="text-align: center;">My goal is to raise $<span id="mygoal">9,999.00</span></div>
<div class="donation-total">Total Donation<span id="total-donation">1,000.00</span></div>
my javascript so far is to get the innerHTML value of mygoal and total-donation.
var mygoal = document.getElementById("mygoal").innerHTML;
var totalgoal = document.getElementById("total-donation").innerHTML;
and I'm getting this as a result:
mygoal = "9,999.00";
total-donation = "1,000.00";
I believe this is a string and not an integer, and using parseInt() only give me the first digit number.
Can anyone give me an idea how can I make this into an integer that can use for computation? example:
mygoal + total-donation = 10,999.00
And also, any idea how can i get the percentage of this two varible?
Use .replace(/,/g,'') to replace commas, then you get the magic of type coercion to convert your string to a number during calculation...
var mygoal = document.getElementById("mygoal").innerHTML.replace(/,/g,'');
var totalgoal = document.getElementById("total-donation").innerHTML.replace(/,/g,'');
If you use + on strings, they will be appended to each other, but other mathematical operators (*/- etc...) will first coerce the strings into numbers. To force coercion, you can multiply by 1, or perhaps use Number("123123.123")...
Number(mygoal) + Number(totalgoal); // using addition, so coerce strings to numbers
(mygoal / total_donation) * 100; // does not need coercion
Your main issue is, that your numbers include colons. The parseFloat() call will work, once you replace these colons. You may use the following code to do so:
// define regexp to replace colons
var replaceColons = new RegExp(',', 'g');
// apply regex
num = num.replace(replaceColons, '');
mygoal=parseInt(mygoal.replace(/,/gi,"")) will give you mygoal=9999.
You should use parseFloat(), not parseInt() ...
More, you have to remove the commas from the string, since parseFloat() does not undertsand number formatting characters (like comma). So, for example:
mygoal = mygoal.replace(/,/g, '');
total_donation = total_donation.replace(/,/g, '');
To get the percentage of two numbers, use:
(mygoal / total_donation) * 100;
Note that in JavaScript you can't use 'minus' char (-) in variables names.
You could use for example 'underscore' char (_), or CamelCase, wich is the recommended style for variables in JavaScript.
You need to convert those Indian (maybe) numbers to valid Javascript numbers for the sum, then convert the output back to the initial format using Number.toLocaleString.
var mygoal = "9,999.00";
var total_donation = "1,000.00";
var total = Number((Number(mygoal.replace(/,/g, '')) + Number(total_donation.replace(/,/g, ''))).toFixed(2));
var finalResult = total.toLocaleString('en-IN',{minimumFractionDigits: 2 });
alert(finalResult);
I was trying with following script
<script src="http://ajax.googleapis.com/ajax/libs/jquery/1.7.1/jquery.min.js"></script>
<script type="text/javascript">
$(document).ready(function() {
$('#item1_number_1').keyup(function() {
var valone = $('#item1_number_1').val();
var valtwo = 5;
var total = ((valone) + (valtwo));
$('#item2_number_1').val(total.toFixed(2));
});
});
</script>
I do not get any result in the field. But when I assign multiple (*) instead of plus (+), I am getting result.
I cannot understand what the error is in "var total = ((valone) + (valtwo));"
You can only call toFixed on Numbers.
String * String will convert the strings to Numbers and multiply them giving you a Number.
String + String will concatenate the two Strings together giving you a String.
You need to convert the strings to Numbers manually before you try to add them together.
var total = (+valone) + (+valtwo);
Then Number + Number will add the two Numbers together giving you a Number.
The value of an input is always a string. "Adding" a string concatenates, giving another string. Strings do not have a toFixed method.
* however is unambiguously "multiply", giving a number and therefore a result.
var valone = parseFloat(document.getElementById('item1_number_1').value);
Use parseInt() to convert fetched value(valone ) to number, and calculate, something like this, please use this only when your number is not float(56.66),
var valone = parseInt($('#item1_number_1').val(), 10);
var valtwo = 5;
var total = ((valone) + (valtwo));
The fetched vaue is treated like string until you convert it into number.
UPDATE
After Archer pointed out, I came to know you are using toFixed() method, which supposed to expect float numbers. So in this case you should use parseFloat() as given below.
var valone = parseFloat($('#item1_number_1').val());
I think one of them is a string. Try parseInt(valone) to make it an int first.
The issue is the + operator can also be used to concat strings together. The * operator is ONLY for multiplication and therefore it implicitly converts your values to numbers.
So you either need to use parseInt, parseFloat, or Number to explicitly convert to a numeric type before using the + operator.
What is the best way to get the number from a string.
The string will always start with n and end with any number i.e.:
n1
n2
n3
n10
n100
n1000
n99999
n9999999999999
and so on.
If you can guarantee the string will always look like that, then
num = parseInt(str.substring(1));
If it always starts with a single 'n', just keep it simple:
var number = parseInt(value.replace('n', ''));
Number.of = function (number) {
if (typeof number === "number")
return number;
var number = number + '',
regnum = /(-)?[0-9]+\.?[0-9]*/.exec(number);
return regnum ? (new Function('return ' + regnum[0]))() : 0;
};
Then just run..
Number.of('n12345'); // 12345
Mine is an incredibly careful approach to it, but what will pull a number out of anything.
Number.of('Hel5lo'); // 5
And always returns a number.
Number.of('There is no number here.'); // 0
That may or may not be helpful to you though.
You can use String.prototype.substr[docs] (or substring) and an unary + to convert the string to a number:
var number = +str.substr(1);
I's suggest:
$('dt').each(
function(){
var n = $(this).text().substring(1);
$('<dd />').text(n).insertAfter($(this));
});
JS Fiddle demo.
It doesn't matter, obviously, which elements you choose to use (I opted for dt and dd for the implied relationship between the input and the output). The important part is the substring() function; the value of 1 refers to the starting point of the resulting substring (from the second character, as JavaScript works with zero-based arrays).
Had a second number been passed, in the form substring(1,4) the resulting substring would have started from the second character and ended with the fifth, unless the string on which substring() is working is of a length shorter than the second argument, in which case it's treated as being equal to the length of the string.
Reference:
substring() at the Mozilla Developer Center.