# Where would I use a bitwise operator in JavaScript?

I've read 'what are bitwise operators?', so I know what bitwise operators are but I'm still not clear on how one might use them. Can anyone offer any real-world examples of where a bitwise operator would be useful in JavaScript?

Thanks.

## Edit:

Just digging into the jQuery source I've found a couple of places where bitwise operators are used, for example: (only the & operator)

``````// Line 2756:
event.which = (event.button & 1 ? 1 : ( event.button & 2 ? 3 : ( event.button & 4 ? 2 : 0 ) ));

// Line 2101
var ret = a.compareDocumentPosition(b) & 4 ? -1 : a === b ? 0 : 1;
`````` Example:

Parses hexadecimal value to get RGB color values.

``````var hex = 'ffaadd';
var rgb = parseInt(hex, 16); // rgb is 16755421

var red   = (rgb >> 16) & 0xFF; // returns 255
var green = (rgb >> 8) & 0xFF;  // 170
var blue  = rgb & 0xFF;     // 221
`````` I heavily use bitwise operators for numerical convertions in production scripts, because sometimes they're much faster than their `Math` or `parseInt` equivalents.

The price I have to pay is code readability. So I usualy use `Math` in development and bitwise in production.

As you can see, browsers don't optimize `Math.ceil` and `parseInt` for years, so I predict bitwise will be faster and shorter way to do things in furure as well.

Bonus: cheat sheet for `| 0` : an easy and fast way to convert anything to integer:

``````( 3|0 ) === 3;             // it does not change integers
( 3.3|0 ) === 3;           // it casts off the fractional part in fractionalal numbers
( 3.8|0 ) === 3;           // it does not round, but exactly casts off the fractional part
( -3.3|0 ) === -3;         // including negative fractional numbers
( -3.8|0 ) === -3;         // which have Math.floor(-3.3) == Math.floor(-3.8) == -4
( "3"|0 ) === 3;           // strings with numbers are typecast to integers
( "3.8"|0 ) === 3;         // during this the fractional part is cast off too
( "-3.8"|0 ) === -3;       // including negative fractional numbers
( NaN|0 ) === 0;           // NaN is typecast to 0
( Infinity|0 ) === 0;      // the typecast to 0 occurs with the Infinity
( -Infinity|0 ) === 0;     // and with -Infinity
( null|0 ) === 0;          // and with null,
( (void 0)|0 ) === 0;      // and with undefined
( []|0 ) === 0;            // and with an empty array
( |0 ) === 3;           // but an array with one number is typecast to number
( [-3.8]|0 ) === -3;       // including the cast off of the fractional part
( [" -3.8 "]|0 ) === -3;   // including the typecast of strings to numbers
( [-3.8, 22]|0 ) === 0     // but an Array with several numbers is typecast to 0
( {}|0 ) === 0;                // an empty object is typecast to 0
( {'2':'3'}|0 ) === 0;         // or a not empty object
( (function(){})|0 ) === 0;    // an empty function is typecast to 0 too
( (function(){ return 3;})|0 ) === 0;
``````

and some magic for me:

``````3 | '0px' === 3;
`````` A real life example :

## `^` bitwise XOR as a `I/O` toggler

Used like `value ^= 1` will change on every call the `value` to `0, 1, 0, 1 ...`

``````function toggle(evt) {
evt.target.IO ^= 1;                                    // Bitwise XOR as 1/0 toggler
evt.target.textContent = evt.target.IO ? "ON" : "OFF"; // Unleash your ideas
}

document.querySelectorAll("button").forEach( el =>
);``````
``````<button>OFF</button>
<button>OFF</button>
<button>OFF</button>`````` Given the advances Javascript is making (especially with nodejs that allows server side programming with js), there is more and more complex code in JS. Here are a couple of instances where I have used bitwise operators:

``````//computes the broadcast address based on the mask and a host address

//converts a number to an ip adress
sprintf(ip, "%i.%i.%i.%i", ((ip_int >> 24) & 0x000000FF),
((ip_int >> 16) & 0x000000FF),
((ip_int >>  8) & 0x000000FF),
( ip_int        & 0x000000FF));
``````

Note: this is C code, but JS is almost identical

• CRC algorithms uses them a lot

Check out the wikipedia entry on this

• Screen resolution operations To tell if a number is odd:

``````function isOdd(number) {
return !!(number & 1);
}

isOdd(1); // true, 1 is odd
isOdd(2); // false, 2 is not odd
isOdd(357); // true, 357 is odd
``````

Faster than modulus - use where performance really counts! Few other examples of how to use bitwise not and double bitwise not:

Floor operation

``````~~2.5    // 2
~~2.1    // 2
~~(-2.5) // -2
``````

Check whether indexOf returned -1 or not

``````var foo = 'abc';
!~foo.indexOf('bar'); // true
`````` You can use them for flipping a boolean value:

``````var foo = 1;
var bar = 0;
``````

This is a bit silly though and for the most part bitwise operators do not have many applications in Javascript. I've used it once for a permissions widget. File permissions in unix are a bitmask, so to parse it, you need to use bit operations. I'm using them to flatten three numbers into 1 as a way of storing multidimensional arrays in a Uint16Array. Here is a snippet of a voxel game I'm developing:

``````function Chunk() {
this._blocks = new Uint16Array(32768);
}

Chunk.prototype.getBlock = function(x, y, z) {
return this._blocks[y + (x << 5) + (z << 10)];
};

Chunk.prototype.setBlock = function(x, y, z, value) {
this._blocks[y + (x << 5) + (z << 10)] = value;
this._networkUpdates.push(value + (y << 15) + (x << 20) + (z << 25));
};

};

Chunk.prototype.processUpdate = function(update) {
// this._blocks[Math.floor(update / 65536)] = update % 65536;
this._blocks[update >> 16] = update & 65535;
};

var chunk = new Chunk();
chunk.setBlock(10, 5, 4); By reading these explanations and running the code snippet an idea can be gained.

``````var hex = 'ffaadd';
var rgb = parseInt(hex, 16); // rgb value is 16755421 in decimal = 111111111010101011011101 in binary = total 24 bits

var red   = (rgb >> 16) & 0xFF; // returns 255
var green = (rgb >> 8) & 0xFF;  // returns 170
var blue  = rgb & 0xFF;         // returns 221

// HOW IS IT

// There are two bitwise operation as named SHIFTING and AND operations.
// SHIFTING is an operation the bits are shifted toward given direction by adding 0 (zero) bit for vacated bit fields.
// AND is an operation which is the same with multiplying in Math. For instance, if 9th bit of the given first bit-set is 0
// and 9th bit of the given second bit-set is 1, the new value will be 0 because of 0 x 1 = 0 in math.

// 0xFF (000000000000000011111111 in binary) - used for to evaluate only last 8 bits of a given another bit-set by performing bitwise AND (&) operation.
// The count of bits is 24 and the first 16 bits of 0xFF value consist of zero (0) value. Rest of bit-set consists of one (1) value.
console.log("0xFF \t\t\t\t: ", 0xFF)

// 111111111010101011011101 -> bits of rgb variable
// 000000000000000011111111 -> 255 after (rgb >> 16) shifting operation
// 000000000000000011111111 -> 255 complement (changes the first 16 bits and does nothing for the last 8 bits)
// 000000000000000011111111 -> result bits after performing bitwise & operation
console.log("Red - (rgb >> 16) & 0xFF \t: ", (rgb >> 16) & 0xFF) // used for to evaluate the first 8 bits

// 111111111010101011011101 -> bits of rgb variable
// 000000001111111110101010 -> 65450 -> 'ffaa'
// 000000000000000011111111 -> 255 complement (changes the first 16 bits and does nothing for the last 8 bits)
// 000000000000000010101010 -> result bits after performing bitwise & operation
// calculation -> 000000001111111110101010 & 000000000000000011111111 = 000000000000000010101010 = 170 in decimal = 'aa' in hex-decimal
console.log("Green - (rgb >> 8) & 0xFF \t: ", (rgb >> 8) & 0xFF) // used for to evaluate the middle 8 bits

// 000000000000000011111111 -> 255 complement (changes the first 16 bits and does nothing for the last 8 bits)
// 000000000000000011011101 -> result bits after performing bitwise & operation
// calculation -> 111111111010101011011101 & 000000000000000011111111 = 221 in decimal = 'dd' in hex-decimal
console.log("Blue - rgb & 0xFF \t\t: ", rgb & 0xFF) // // used for to evaluate the last 8 bits.

console.log("It means that `FFAADD` hex-decimal value specifies the same color with rgb(255, 170, 221)")

/* console.log(red)
console.log(green)
console.log(blue) */`````` They seem to be very useful when you work with hex values and bits. Since 4 bits can represent 0 to F.

1111 = F 1111 1111 = FF. Example using Node.js

Presuming you had a file (called multiply.js) with these contents, you could run

```````node multiply <number> <number>`
``````

and get an output consistent with using the multiplication operator on the same two numbers. The bit shifting going on in the `Mulitply` function is an example of how to take the bit mask representing one number and use it to flip bits in another number for fast operations.

``````var a, b, input = process.argv.slice(2);

var printUsage = function() {
console.log('USAGE:');
console.log('  node multiply <number> <number>');
}

if(input === '--help') {+
printUsage();
process.exit(0);
}

if(input.length !== 2) {
printUsage();
process.exit(9);
}

if(isNaN(+input) || isNaN(+input)) {
printUsage();
process.exit(9);
}

// Okay, safe to proceed

a = parseInt(input),
b = parseInt(input);

var Multiply = function(a,b) {
var x = a, y = b, z = 0;

while( x > 0 ) {
if(x % 2 === 1) {
z = z + y;
}
y = y << 1;
x = x >> 1;
}

return z;
}

var result = Multiply(a,b);

console.log(result);
`````` I just found this question trying to confirm if the bitwise `AND` operator also was `&` in Javascript.

Since you asked for an example:

``````if (\$('input[id="user[privileges]"]').length > 0) {
\$('#privileges button').each(function () {
if (parseInt(\$('input[id="user[privileges]"]').val()) & parseInt(\$(this).attr('value'))) {
\$(this).button('toggle');
}
});
}
``````

It populates the state of buttons with jQuery given a bitmask value of a hidden field:

• `none` = `0`
• `user` = `1`
• `administrator` = `2`
• `user` + `administrator` = `3` In JavaScript, you can use a double bitwise negation (`~~n`) as a replacement for `Math.floor(n)` (if `n` is a positive number) or `parseInt(n, 10)` (even if `n` is negative). `n|n` and `n&n` always yield the same results as `~~n`.

``````var n = Math.PI;
n; // 3.141592653589793
Math.floor(n); // 3
parseInt(n, 10); // 3
~~n; // 3
n|n; // 3
n&n; // 3

// ~~n works as a replacement for parseInt() with negative numbers…
~~(-n); // -3
(-n)|(-n); // -3
(-n)&(-n); // -3
parseInt(-n, 10); // -3
// …although it doesn’t replace Math.floor() for negative numbers
Math.floor(-n); // -4
``````

A single bitwise negation (`~`) calculates `-(parseInt(n, 10) + 1)`, so two bitwise negations will return `-(-(parseInt(n, 10) + 1) + 1)`.

It should be noted that of these three alternatives, `n|n` appears to be the fastest.

Update: More accurate benchmarks here: http://jsperf.com/rounding-numbers-down

(As posted on Strangest language feature) ``````var arr = ['abc', 'xyz']
``````

Annoyed to write

``````if (arr.indexOf('abc') > -1) {
// 'abc' is in arr
}

if (arr.indexOf('def') === -1) {
// 'def' is not in arr
}
``````

to check if something is inside an array?

You can use the bitwise operator `~` like so:

``````if (~arr.indexOf('abc')) {
// 'abc' is in arr
}

if (! ~arr.indexOf('def')) {
// 'def' is not in arr
}
`````` Used extensively, for example, in JS events.