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What is the "double tilde" (~~) operator in JavaScript?
The "double tilde" (~~) operator is a double NOT bitwise operator in JavaScript. It converts a number to a 32-bit signed integer and truncates any decimal part, making it a faster alternative to Math.floor() for positive numbers.
How It Works
The tilde (~) operator performs bitwise NOT operation. When used twice (~~), it effectively converts a value to an integer by:
- Converting the value to a 32-bit signed integer
- Truncating decimal places (not rounding)
- Returning the integer result
Example: Basic Usage
<html>
<body>
<script>
var a = 2.7;
var b, c, d;
b = ~~a; // Double tilde
c = Math.floor(a); // Math.floor()
d = ~~a === Math.floor(a);
document.write("Original: " + a);
document.write("<br>Double tilde: " + b);
document.write("<br>Math.floor: " + c);
document.write("<br>Are equal: " + d);
</script>
</body>
</html>
Original: 2.7 Double tilde: 2 Math.floor: 2 Are equal: true
Difference with Negative Numbers
The key difference between ~~ and Math.floor() appears with negative numbers:
<html>
<body>
<script>
var negative = -2.7;
document.write("Original: " + negative);
document.write("<br>~~ operator: " + ~~negative);
document.write("<br>Math.floor: " + Math.floor(negative));
document.write("<br>Math.trunc: " + Math.trunc(negative));
</script>
</body>
</html>
Original: -2.7 ~~ operator: -2 Math.floor: -3 Math.trunc: -2
Comparison Table
| Input | ~~ operator | Math.floor() | Math.trunc() |
|---|---|---|---|
| 2.7 | 2 | 2 | 2 |
| -2.7 | -2 | -3 | -2 |
| 5.9 | 5 | 5 | 5 |
Performance Note
While ~~ was historically faster than Math.floor(), modern JavaScript engines have optimized Math.floor() significantly. The performance difference is now negligible, and Math.floor() or Math.trunc() are more readable.
Conclusion
The double tilde (~~) operator truncates decimal places and works like Math.trunc(). While it's a clever shortcut, prefer Math.floor() or Math.trunc() for better code readability and clarity.
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