JavaScript Bit Manipulation Cheat Sheet

To convert a number to its binary representation in JavaScript, you can use the toString method with a base of 2. Here’s how you can do it:

  let num = 5;
  let binaryString = num.toString(2);
  console.log(binaryString); // "101"

If you need a fixed-length binary string, you can pad the result with leading zeros:

let num = 5;
let binaryString = num.toString(2).padStart(8, '0');
console.log(binaryString); // "00000101"

Basic Operators

1. AND (&)

   • Description: Returns a 1 in each bit position for which the corresponding bits of both operands are 1. The AND operator is commonly used for masking and checking the presence of specific bits.
   • Example: 5 & 3 → 0101 & 0011 → 0001 (1)

2. OR (|)

   • Description: Returns a 1 in each bit position for which the corresponding bits of either operand are 1. The OR operator is useful for combining or merging bits.
   • Example: 5 | 3 → 0101 | 0011 → 0111 (7)

3. XOR (^)

   • Description: Returns a 1 in each bit position for which the corresponding bits of either but not both operands are 1. The XOR operator is often used for toggling or swapping bits.
   • Example: 5 ^ 3 → 0101 ^ 0011 → 0110 (6)

4. NOT (~)

   • Description: Inverts the bits of the operand (flips 0s to 1s and 1s to 0s). This operator is useful for inverting the bits of a number.
   • Example: ~5 → ~0101 → 1010 (Note: in JavaScript, the result is signed and depends on the bit length.)

Shift Operators

1. Left Shift (<<)

   • Description: Shifts the bits of the operand to the left by the specified number of positions. This operation is equivalent to multiplying the number by 2 raised to the power of the shift amount. It is frequently used for efficient multiplication or creating space for additional bits.
   • Example: 5 << 2 → 0101 << 2 → 10100 (20)

2. Sign-Propagating Right Shift (>>)

   • Description: Shifts the bits of the operand to the right by the specified number of positions, preserving the sign. This operation is equivalent to dividing the number by 2 raised to the power of the shift amount. It is commonly used for efficient division or extracting specific bits.
   • Example: 5 >> 1 → 0101 >> 1 → 0010 (2)

3. Zero-Fill Right Shift (>>>)

   • Description: Shifts the bits of the operand to the right by the specified number of positions, filling with zeros.
   • Example: 5 >>> 1 → 0101 >>> 1 → 0010 (2)

Common Bit Manipulation Tasks

1. Check if a number is even or odd

   • Description: Use the AND operator with 1.
   • Example: num & 1 → 0 (even), 1 (odd)
   • Code:

     function isOdd(num) {
         return (num & 1) === 1;
     }

2. Set a specific bit

   • Description: Use the OR operator with a bit mask.
   • Example: To set the 2nd bit of 5 (0101):
   • Code:

     function setBit(num, bitPosition) {
         return num | (1 << bitPosition);
     }

3. Clear a specific bit

   • Description: Use the AND operator with a NOT bit mask.
   • Example: To clear the 2nd bit of 5 (0101):
   • Code:

     function clearBit(num, bitPosition) {
         return num & ~(1 << bitPosition);
     }

4. Toggle a specific bit

   • Description: Use the XOR operator with a bit mask.
   • Example: To toggle the 2nd bit of 5 (0101):
   • Code:

     function toggleBit(num, bitPosition) {
         return num ^ (1 << bitPosition);
     }

5. Check if a specific bit is set

   • Description: Use the AND operator with a bit mask.
   • Example: To check the 2nd bit of 5 (0101):
   • Code:

     function isBitSet(num, bitPosition) {
         return (num & (1 << bitPosition)) !== 0;
     }

6. Count the number of 1s (Hamming weight)

   • Description: Use a loop or the built-in toString(2) and match method.
   • Code:

     function countSetBits(num) {
         let count = 0;
         while (num) {
             count += num & 1;
             num >>= 1;
         }
         return count;
     }
     
     // Alternatively
     function countSetBits(num) {
         return num.toString(2).split('0').join('').length;
     }

7. Flip all bits

   • Description: Use the NOT operator.
   • Example: To flip all bits of 5 (0101):
   • Code:

     function flipBits(num) {
         return ~num;
     }