Bitwise AND Assignment

The &= (bitwise AND assignment) operator performs a bitwise AND operation between the binary representations of its left and right operands, assigning the computed 32-bit integer result back to the left operand.

x &= y;
// Equivalent to: x = x & y;

Mechanical Behavior

1. Type Coercion (ToInt32): Before the operation occurs, the TypeScript/JavaScript runtime implicitly coerces both operands into 32-bit signed integers. Fractional values are truncated.
2. Bitwise Evaluation: The operator compares the operands bit by bit. A bit in the resulting integer is set to 1 if and only if the corresponding bits in both operands are 1. If either bit is 0, the resulting bit is 0.
3. Assignment: The newly calculated 32-bit integer is assigned to the memory location of the left operand.

Truth Table

Bit A (Left)	Bit B (Right)	Result (A & B)
1	1	1
1	0	0
0	1	0
0	0	0

Execution Example

let a: number = 14; // Binary: 00000000 00000000 00000000 00001110
let b: number = 9;  // Binary: 00000000 00000000 00000000 00001001

a &= b; 

// Bitwise Calculation:
//   00001110 (14)
// & 00001001 (9)
// -------
//   00001000 (8)

console.log(a); // Output: 8

TypeScript Compiler Constraints

While the underlying JavaScript engine will attempt to coerce any type into a number for bitwise operations, the TypeScript compiler enforces strict type safety:

• Operand Types: TypeScript requires both the left and right operands to be of type number (or any). Attempting to use &= with strings, booleans, or objects will throw a compilation error (e.g., TS2362: The left-hand side of an arithmetic operation must be of type 'any', 'number', 'bigint' or an enum type.).
• Mutability: The left operand must be a mutable reference. It cannot be a constant (const) or a read-only property.
• BigInt Support: The &= operator also supports bigint types, provided both operands are bigint. Mixing number and bigint will result in a TS2365 compiler error. When operating on bigint, the operation is not restricted to 32 bits.

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