Develop Reference

What does it mean that shift operators “drop any bits beyond the 5th”?

From the book “JavaScript: The Definitive Guide”:
The bitwise operators expect integer operands and behave as if those values were represented as 32-bit integers rather than 64-bit floating-point values.
These operators convert their operands to numbers, if necessary, and then coerce the numeric values to 32-bit integers by dropping any fractional part and any bits beyond the 32nd.
The shift operators require a right-side operand between 0 and 31.
After converting this operand to an unsigned 32-bit integer, they drop any bits beyond the 5th, which yields a number in the appropriate range.
Surprisingly, NaN, Infinity, and -Infinity all convert to 0 when used as operands of these bitwise operators.
I can’t understand the sentence “After converting this operand to an unsigned 32-bit integer, they drop any bits beyond the 5th, which yields a number in the appropriate range.”.
Does the fifth number have any meaning? I’m seeking for proper examples.

The shift operators require a right-side operand between 0 and 31.
Meaning the right-side operand will be between 0b00000 and 0b11111 in binary form, so 5 bits.

XOR operator in javascript different from XOR operator in python

I am trying to replicate some javascript code into python, and for some reason the XOR operator (^) in javascript gives me a different value than the XOR operator (^) in python. I have an example below. I know the values should be different because of Math.random(), but why is it like 4 significant digits longer?
Javascript:
console.log(Math.floor(2147483648 * Math.random()) ^ 1560268851466)
= 1596700165
Python:
import math
math.floor(2147483648 * random.random()) ^ 1560268851466
= 1559124407072

Your Python result is correct, given XOR's input bits. Your longer operand is on the order of 2^40, and so is your final result.
The Javascript result has been truncated to 32 bits, the shorter operand.

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Bitwise_Operators:
Bitwise operators treat their operands as a sequence of 32 bits (zeroes and ones), rather than as decimal, hexadecimal, or octal numbers. For example, the decimal number nine has a binary representation of 1001. Bitwise operators perform their operations on such binary representations, but they return standard JavaScript numerical values.
However the particular code you are using can be "fixed" via XOR-ing the 32-bit part of your number, and simply adding the rest:
// 1560268851466 = 0x16B_4745490A
console.log( (Math.floor(2147483648 * Math.random()) ^ 0x4745490A) + 0x16B00000000);
(As 2147483648 is 0x8000000, the random part is "fine", it does not get truncated)

Numeric conversion in JavaScript [duplicate]

How do parseInt() and Number() behave differently when converting strings to numbers?

Well, they are semantically different, the Number constructor called as a function performs type conversion and parseInt performs parsing, e.g.:
// parsing:
parseInt("20px"); // 20
parseInt("10100", 2); // 20
parseInt("2e1"); // 2
// type conversion
Number("20px"); // NaN
Number("2e1"); // 20, exponential notation
Also parseInt will ignore trailing characters that don't correspond with any digit of the currently used base.
The Number constructor doesn't detect implicit octals, but can detect the explicit octal notation:
Number("010"); // 10
Number("0o10") // 8, explicit octal
parseInt("010"); // 8, implicit octal
parseInt("010", 10); // 10, decimal radix used
And it can handle numbers in hexadecimal notation, just like parseInt:
Number("0xF"); // 15
parseInt("0xF"); //15
In addition, a widely used construct to perform Numeric type conversion, is the Unary + Operator (p. 72), it is equivalent to using the Number constructor as a function:
+"2e1"; // 20
+"0xF"; // 15
+"010"; // 10

typeof parseInt("123") => number
typeof Number("123") => number
typeof new Number("123") => object (Number primitive wrapper object)
first two will give you better performance as it returns a primitive instead of an object.

One minor difference is what they convert of undefined or null,
Number() Or Number(null) Or Number('') // returns 0
while
parseInt() Or parseInt(null) // returns NaN

Summary:
parseInt():
Takes a string as a first argument, the radix (An integer which is the base of a numeral system e.g. decimal 10 or binary 2) as a second argument
The function returns a integer number, if the first character cannot be converted to a number NaN will be returned.
If the parseInt() function encounters a non numerical value, it will cut off the rest of input string and only parse the part until the non numerical value.
If the radix is undefined or 0, JS will assume the following:
If the input string begins with "0x" or "0X", the radix is 16 (hexadecimal), the remainder of the string is parsed into a number.
If the input value begins with a 0 the radix can be either 8 (octal) or 10 (decimal). Which radix is chosen is depending on JS engine implementation. ES5 specifies that 10 should be used then. However, this is not supported by all browsers, therefore always specify radix if your numbers can begin with a 0.
If the input value begins with any number, the radix will be 10
Number():
The Number() constructor can convert any argument input into a number. If the Number() constructor cannot convert the input into a number, NaN will be returned.
The Number() constructor can also handle hexadecimal number, they have to start with 0x.
Example:
console.log(parseInt('0xF', 16)); // 15
// z is no number, it will only evaluate 0xF, therefore 15 is logged
console.log(parseInt('0xFz123', 16));
// because the radix is 10, A is considered a letter not a number (like in Hexadecimal)
// Therefore, A will be cut off the string and 10 is logged
console.log(parseInt('10A', 10)); // 10
// first character isnot a number, therefore parseInt will return NaN
console.log(parseInt('a1213', 10));
console.log('\n');
// start with 0X, therefore Number will interpret it as a hexadecimal value
console.log(Number('0x11'));
// Cannot be converted to a number, NaN will be returned, notice that
// the number constructor will not cut off a non number part like parseInt does
console.log(Number('123A'));
// scientific notation is allowed
console.log(Number('152e-1')); // 15.21

If you are looking for performance then probably best results you'll get with bitwise right shift "10">>0. Also multiply ("10" * 1) or not not (~~"10"). All of them are much faster of Number and parseInt.
They even have "feature" returning 0 for not number argument.
Here are Performance tests.

I found two links of performance compare among several ways of converting string to int.
parseInt(str,10)
parseFloat(str)
str << 0
+str
str*1
str-0
Number(str)
http://jsben.ch/#/zGJHM
http://phrogz.net/js/string_to_number.html

parseInt() -> Parses a number to specified redix.
Number()-> Converts the specified value to its numeric equivalent or NaN if it fails to do so.
Hence for converting some non-numeric value to number we should always use Number() function.
eg.
Number("")//0
parseInt("")//NaN
Number("123")//123
parseInt("123")//123
Number("123ac") //NaN,as it is a non numeric string
parsInt("123ac") //123,it parse decimal number outof string
Number(true)//1
parseInt(true) //NaN
There are various corner case to parseInt() functions as it does redix conversion, hence we should avoid using parseInt() function for coersion purposes.
Now, to check weather the provided value is Numeric or not,we should use nativeisNaN() function

I always use parseInt, but beware of leading zeroes that will force it into octal mode.

It's a good idea to stay away from parseInt and use Number and Math.round unless you need hex or octal. Both can use strings. Why stay away from it?
parseInt(0.001, 10)
0
parseInt(-0.0000000001, 10)
-1
parseInt(0.0000000001, 10)
1
parseInt(4000000000000000000000, 10)
4
It completely butchers really large or really small numbers. Oddly enough it works normally if these inputs are a string.
parseInt("-0.0000000001", 10)
0
parseInt("0.0000000001", 10)
0
parseInt("4000000000000000000000", 10)
4e+21
Instead of risking hard to find bugs with this and the other gotchas people mentioned, I would just avoid parseInt unless you need to parse something other than base 10. Number, Math.round, Math.floor, and .toFixed(0) can all do the same things parseInt can be used for without having these types of bugs.
If you really want or need to use parseInt for some of it's other qualities, never use it to convert floats to ints.

parseInt converts to a integer number, that is, it strips decimals. Number does not convert to integer.

Another way to get the result is to use the ~ operator
For most circumstances
~~someThing === parseInt(something)
but ~~ will return zero for strings that parseInt will accept with trailing other characters or with the number base spec (eg hex) and will also return zero when parseInt returns NaN. Another difference is that ~~ if given a bigint returns a bigint to which you can add another bigint whereas parseInt returns an ordinary floating point number (yes really - it gives exactly the same value as parseFloat) if the bigint is large
However for most circumstances ~~ is 30% faster than parseInt. It is only slower by 10% when something is a floating point represented as a string.
So if the more restricted scope of ~~ fits your need then save the computer time and give yourself less to type

Is it correct to set bit 31 in javascript?

When I try to set 31 bit 0 | 1 << 31 I get the following result:
console.log(0 | 1 << 31); // -2147483648
Which is actualy:
console.log((-2147483648).toString(2)) // -10000000000000000000000000000000
Is it correct to set 31 bit or should I restrict to 30 to prevent negative values?

Refer to ECMA5 that the bitwise operators and shift operators operate on 32-bit ints, so in that case, the max safe integer is 2^31-1, or 2147483647.
Here is one explanation.
The << operator is defined as working on signed 32-bit integers (converted from the native Number storage of double-precision float). So 1<<31 must result in a negative number.
The only JavaScript operator that works using unsigned 32-bit integers is >>>. You can exploit this to convert a signed-integer-in-Number you've been working on with the other bitwise operators to an unsigned-integer-in-Number:
(1<<31)>>>0

Most bitwise operations are specified as converting their operands to signed 32-bit integers. It is perfectly correct to use bit 31, but yes, you'll get negative values. Usually it doesn't matter if you're doing bitwise operations anyway, since all you (should) care about is the bit pattern, not the decimal value of the number.
If you do want a positive value back, you can convert it back with >>> 0, because >>> is specified to convert its operands to unsigned 32-bit integers.
console.log((0 | 1 << 31) >>> 0);

Why does string to number comparison work in Javascript

I am trying to compare a value coming from a HTML text field with integers. And it works as expected.
Condition is -
x >= 1 && x <= 999;
Where x is the value of text field. Condition returns true whenever value is between 1-999 (inclusive), else false.
Problem is, that the value coming from the text field is of string type and I'm comparing it with integer types. Is it okay to have this comparison like this or should I use parseInt() to convert x to integer ?

Because JavaScript defines >= and <= (and several other operators) in a way that allows them to coerce their operands to different types. It's just part of the definition of the operator.
In the case of <, >, <=, and >=, the gory details are laid out in §11.8.5 of the specification. The short version is: If both operands are strings (after having been coerced from objects, if necessary), it does a string comparison. Otherwise, it coerces the operands to numbers and does a numeric comparison.
Consequently, you get fun results, like that "90" > "100" (both are strings, it's a string comparison) but "90" < 100 (one of them is a number, it's a numeric comparison). :-)
Is it okay to have this comparison like this or should I use parseInt() to convert x to integer ?
That's a matter of opinion. Some people think it's totally fine to rely on the implicit coercion; others think it isn't. There are some objective arguments. For instance, suppose you relied on implicit conversion and it was fine because you had those numeric constants, but later you were comparing x to another value you got from an input field. Now you're comparing strings, but the code looks the same. But again, it's a matter of opinion and you should make your own choice.
If you do decide to explicitly convert to numbers first, parseInt may or may not be what you want, and it doesn't do the same thing as the implicit conversion. Here's a rundown of options:
parseInt(str[, radix]) - Converts as much of the beginning of the string as it can into a whole (integer) number, ignoring extra characters at the end. So parseInt("10x") is 10; the x is ignored. Supports an optional radix (number base) argument, so parseInt("15", 16) is 21 (15 in hex). If there's no radix, assumes decimal unless the string starts with 0x (or 0X), in which case it skips those and assumes hex. Does not look for the new 0b (binary) or 0o (new style octal) prefixes; both of those parse as 0. (Some browsers used to treat strings starting with 0 as octal; that behavior was never specified, and was [specifically disallowed][2] in the ES5 specification.) Returns NaN if no parseable digits are found.
Number.parseInt(str[, radix]) - Exactly the same function as parseInt above. (Literally, Number.parseInt === parseInt is true.)
parseFloat(str) - Like parseInt, but does floating-point numbers and only supports decimal. Again extra characters on the string are ignored, so parseFloat("10.5x") is 10.5 (the x is ignored). As only decimal is supported, parseFloat("0x15") is 0 (because parsing ends at the x). Returns NaN if no parseable digits are found.
Number.parseFloat(str) - Exactly the same function as parseFloat above.
Unary +, e.g. +str - (E.g., implicit conversion) Converts the entire string to a number using floating point and JavaScript's standard number notation (just digits and a decimal point = decimal; 0x prefix = hex; 0b = binary [ES2015+]; 0o prefix = octal [ES2015+]; some implementations extend it to treat a leading 0 as octal, but not in strict mode). +"10x" is NaN because the x is not ignored. +"10" is 10, +"10.5" is 10.5, +"0x15" is 21, +"0o10" is 8 [ES2015+], +"0b101" is 5 [ES2015+]. Has a gotcha: +"" is 0, not NaN as you might expect.
Number(str) - Exactly like implicit conversion (e.g., like the unary + above), but slower on some implementations. (Not that it's likely to matter.)
Bitwise OR with zero, e.g. str|0 - Implicit conversion, like +str, but then it also converts the number to a 32-bit integer (and converts NaN to 0 if the string cannot be converted to a valid number).
So if it's okay that extra bits on the string are ignored, parseInt or parseFloat are fine. parseInt is quite handy for specifying radix. Unary + is useful for ensuring the entire string is considered. Takes your choice. :-)
For what it's worth, I tend to use this function:
const parseNumber = (str) => str ? +str : NaN;
(Or a variant that trims whitespace.) Note how it handles the issue with +"" being 0.
And finally: If you're converting to number and want to know whether the result is NaN, you might be tempted to do if (convertedValue === NaN). But that won't work, because as Rick points out below, comparisons involving NaN are always false. Instead, it's if (isNaN(convertedValue)).

The MDN's docs on Comparision states that the operands are converted to a common type before comparing (with the operator you're using):
The more commonly used abstract comparison (e.g. ==) converts the operands to the same Type before making the comparison. For relational abstract comparisons (e.g., <=), the operands are first converted to primitives, then to the same type, before comparison.
You'd only need to apply parseInt() if you were using a strict comparision, that does not perform the auto casting before comparing.

You should use parseInt if the var is a string. Add = to compare datatype value:
parseInt(x) >== 1 && parseInt(x) <== 999;