Bit Operations

Here are concise notes on using bitwise operators in JavaScript — useful for interviews and coding practice:

🔹 Basics

JavaScript stores numbers as 64-bit floating point, but bitwise operators work on 32-bit signed integers.

Signed 32-bit integer → range: -2,147,483,648 to 2,147,483,647
Bitwise ops truncate numbers to 32-bit, then back to JS Number.

🔹 Common Bitwise Operators

Operator	Symbol	Example	Meaning
AND	`&`	`5 & 3 = 1`	Bit is `1` only if both bits are `1`
OR	`\|`	`5 \| 3 = 7`	Bit is `1` if at least one bit is `1`
XOR	`^`	`5 ^ 3 = 6`	Bit is `1` if bits differ
NOT	`~`	`~5 = -6`	Flips all bits (2’s complement)
Left Shift	`<<`	`5 << 1 = 10`	Shift left, fill with 0
Right Shift (Sign-propagating)	`>>`	`5 >> 1 = 2`	Shift right, keep sign bit
Unsigned Right Shift	`>>>`	`-5 >>> 1 = 2147483645`	Shift right, fill with 0

🔹 Useful Tricks

Check even/odd

let x = 7;
console.log(x & 1 ? "Odd" : "Even"); // Odd

Swap two numbers without temp

let a = 5, b = 9;
a = a ^ b;
b = a ^ b;
a = a ^ b;
console.log(a, b); // 9, 5

Multiply or divide by 2

console.log(5 << 1); // 10  (5 * 2)
console.log(20 >> 2); // 5  (20 / 4)

Check if k-th bit is set

let n = 13; // 1101
let k = 2;  // (0-indexed from right)
console.log((n & (1 << k)) !== 0); // true (bit is set)

Set a bit

n = n | (1 << k);

Clear a bit

n = n & ~(1 << k);

Toggle a bit

n = n ^ (1 << k);

Count set bits (Brian Kernighan’s Algo)

function countBits(n) {
  let count = 0;
  while (n > 0) {
    n = n & (n - 1); // clears the lowest set bit
    count++;
  }
  return count;
}
console.log(countBits(29)); // 4 (11101 has 4 set bits)

🔹 Common Use Cases

Checking even/odd quickly
Efficient multiplication/division by powers of 2
Bit masking (checking flags/permissions)
Swapping numbers without temp variable
Subset generation problems
Low-level optimizations in algorithms