JavaScript Bitwise operators


Example

Note that all bitwise operations operate on 32-bit integers by passing any operands to the internal function ToInt32.

Bitwise or

var a;
a = 0b0011 | 0b1010; // a === 0b1011
// truth table
// 1010 | (or)
// 0011  
// 1011  (result)

Bitwise and

a = 0b0011 & 0b1010; // a === 0b0010
// truth table
// 1010 & (and)
// 0011  
// 0010  (result)

Bitwise not

a = ~0b0011; // a === 0b1100
// truth table
// 10 ~(not)
// 01  (result)

Bitwise xor (exclusive or)

a = 0b1010 ^ 0b0011; // a === 0b1001
// truth table
// 1010 ^ (xor)
// 0011  
// 1001  (result)

Bitwise left shift

a = 0b0001 << 1; // a === 0b0010
a = 0b0001 << 2; // a === 0b0100
a = 0b0001 << 3; // a === 0b1000

Shift left is equivalent to integer multiply by Math.pow(2, n). When doing integer math, shift can significantly improve the speed of some math operations.

var n = 2;
var a = 5.4;
var result = (a << n) === Math.floor(a) * Math.pow(2,n);
// result is true
a = 5.4 << n; // 20

Bitwise right shift >> (Sign-propagating shift) >>> (Zero-fill right shift)

a = 0b1001 >> 1; // a === 0b0100
a = 0b1001 >> 2; // a === 0b0010
a = 0b1001 >> 3; // a === 0b0001

a = 0b1001 >>> 1; // a === 0b0100
a = 0b1001 >>> 2; // a === 0b0010
a = 0b1001 >>> 3; // a === 0b0001

A negative 32bit value always has the left most bit on:

a = 0b11111111111111111111111111110111 | 0;   
console.log(a); // -9
b = a >> 2;     // leftmost bit is shifted 1 to the right then new left most bit is set to on (1)
console.log(b); // -3
b = a >>> 2;    // leftmost bit is shifted 1 to the right. the new left most bit is set to off (0)
console.log(b); // 2147483643

The result of a >>> operation is always positive.
The result of a >> is always the same sign as the shifted value.

Right shift on positive numbers is the equivalent of dividing by the Math.pow(2,n) and flooring the result:

a = 256.67;
n = 4;
result = (a >> n) === Math.floor( Math.floor(a) / Math.pow(2,n) );
// result is true
a = a >> n; //  16

result = (a >>> n) === Math.floor( Math.floor(a) / Math.pow(2,n) );
// result is true
a = a >>> n; //  16

Right shift zero fill (>>>) on negative numbers is different. As JavaScript does not convert to unsigned ints when doing bit operations there is no operational equivalent:

a = -256.67;
result = (a >>> n) === Math.floor( Math.floor(a) / Math.pow(2,n) );
// result is false

Bitwise assignment operators

With the exception of not (~) all the above bitwise operators can be used as assignment operators:

a |= b;   // same as: a = a | b;
a ^= b;   // same as: a = a ^ b;
a &= b;   // same as: a = a & b;
a >>= b;  // same as: a = a >> b;
a >>>= b; // same as: a = a >>> b;
a <<= b;  // same as: a = a << b;

Warning: Javascript uses Big Endian to store integers. This will not always match the Endian of the device/OS. When using typed arrays with bit lengths greater than 8 bits you should check if the environment is Little Endian or Big Endian before applying bitwise operations.

Warning: Bitwise operators such as & and | are not the same as the logical operators && (and) and || (or). They will provide incorrect results if used as logical operators. The ^ operator is not the power operator (ab).