## What Does the Double Tilde Operator (~~) Actually Do in JavaScript?

Unveiling the True Nature of Double Tilters (~~) in JavaScript

In the realm of JavaScript, the operator stands out with its enigmatic functionality. It's commonly known that the single tilde (~) signifies bitwise NOT, leaving us pondering: what does its doublett () achieve?

Contrary to the intuition that it doubles the bitwise negation, the ~~ operator has a surprising effect. It has the ability to truncate the decimal part of a number, effectively rounding it towards the closest whole number.

Behind the scenes, the ~~ operator operates by treating its operand as a signed 32-bit integer, performing bitwise operations regardless of the operand's actual type (number, string, etc.). As a result, the fractional part is discarded, and the result is always a number.

Precisely, the ~~ operator essentially simulates the following function:

function truncate(x) {
  if(x < 0) return Math.ceil(x);
  else return Math.floor(x);
}

However, this operation holds true only if the value of x falls within the range of -(2^31) to 2^31 - 1, inclusive. Outside this range, overflow may occur, leading to unpredictable results.

While ~~ can come in handy for swiftly converting string arguments to numbers, its limitations (possibility of overflow and incorrect behavior for non-integer values) make it less desirable for numerical manipulation. Instead, it's generally preferable to use x or Number(x) for these purposes.

Deciphering Double Negation

Understanding the ~~ operator as the negation of a negation requires a deeper dive into binary representation. Take the number -43.2 as an example, represented in signed (two's complement) 32-bit binary form:

-43.2<sub>10</sub> = 11111111111111111111111111010101<sub>2</sub>

Inverting all the bits (bitwise NOT) produces:

NOT -43<sub>10</sub> = 00000000000000000000000000101010<sub>2</sub> = 42<sub>10</sub>

Applying the negation once more results in:

NOT 42<sub>10</sub> = 11111111111111111111111111010101<sub>2</sub> = -43<sub>10</sub>

This final result (-43) differs from the result of Math.floor(-43.2), which would be -44. This is because ~~ rounds numbers away from zero, unlike Math.floor, which rounds down.

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