Math.trunc()
ES6+Returns the integer part of a number by removing any fractional digits.
Syntax
Math.trunc(x)Parameters
x number A number
Return Value
The integer part of the given number
Examples
console.log(Math.trunc(4.7));
console.log(Math.trunc(-4.7));
console.log(Math.trunc(0.123));📌 When to Use
Use Math.trunc() when you need to remove decimals without rounding, especially for negative numbers where the behavior differs from Math.floor().
⚠️ Common Mistakes
Using Math.trunc() in environments that do not support ES6 without a polyfill.
Confusing Math.trunc() with parseInt() - they behave differently with non-numeric strings.
✅ Best Practices
Use Math.trunc() instead of parseInt(x, 10) when you already have a number and just need to remove decimals.
For ES5 compatibility, use Math.floor() for positive numbers and Math.ceil() for negative numbers.
⚡ Performance Notes
Math.trunc() is faster than parseInt() for numeric values. The bitwise (x | 0) trick is faster but limited to 32-bit integers.
🌍 Real World Example
Video Timestamp Formatter
Convert video duration in seconds to hours:minutes:seconds format.
function formatDuration(totalSeconds) {
const hours = Math.trunc(totalSeconds / 3600);
const minutes = Math.trunc((totalSeconds % 3600) / 60);
const seconds = Math.trunc(totalSeconds % 60);
const pad = (n) => String(n).padStart(2, '0');
if (hours > 0) {
return `${hours}:${pad(minutes)}:${pad(seconds)}`;
}
return `${minutes}:${pad(seconds)}`;
}
console.log(formatDuration(3725.8)); // "1:02:05"
console.log(formatDuration(185.4)); // "3:05"