Double Tilde Operator in JavaScript (~~)

In JavaScript, the ~~ operator is a type coercion operator that removes everything after the decimal point of a number. This differs from the ~ operator, which is a bitwise NOT operator that inverts the bits of a value.

Operation

The operator works by first converting its operand to a signed 32-bit integer. This means that even if the operand is a floating-point number or a string, it will be treated as an integer internally. The operator effectively performs the following:

• If the operand is negative, it rounds up to the next integer (Math.ceil).
• If the operand is positive, it rounds down to the next integer (Math.floor).

Usefulness

While the ~~ operator may seem like a simple replacement for Math.floor or Math.ceil, it has some limitations:

• It can result in overflow if the operand is outside the range of -(2^31) to 2^31 - 1.
• It is not suitable for non-integer operands, as it ignores the decimal portion.

Therefore, it is generally recommended to use x (unary plus) or Number(x) for type coercion, and Math.floor or Math.ceil for rounding.

Example

Consider the number -43.2:

• ~~(-43.2) = -43
• Math.floor(-43.2) = -44

As you can see, ~~ rounds toward zero while Math.floor rounds down. This behavior can be useful in certain scenarios, such as truncating a number without using a decimal point.