javascript trunc() function

user_139361 0
Viewed 33624

I want to truncate a number in javascript, that means to cut away the decimal part:

trunc ( 2.6 ) == 2

trunc (-2.6 ) == -2

After heavy benchmarking my answer is:

 function trunc (n) {
    return ~~n;
 }
 
 // or  

 function trunc1 (n) {
    return n | 0;
 }
bitwise-operators bit-manipulation javascript
5 Answers

As an addition to the @Daniel's answer, if you want to truncate always towards zero, you can:

function truncate(n) {
  return n | 0; // bitwise operators convert operands to 32-bit integers
}

Or: 

function truncate(n) {
  return Math[n > 0 ? "floor" : "ceil"](n);
}

Both will give you the right results for both, positive and negative numbers:

truncate(-3.25) == -3;
truncate(3.25) == 3;
CMS_54450

For positive numbers:

Math.floor(2.6) == 2;

For negative numbers:

Math.ceil(-2.6) == -2;
user_2229080

In case it wasn't available before and for anyone else who stumbles upon this thread, you can now simply use the trunc() function from the Math library, like so:

let x = -201;
x /= 10;
console.log(x);
console.log(Math.trunc(x));

>>> -20.1
>>> -20
user_23802730
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