javascript trunc() function

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

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;
 }

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;

For positive numbers:

Math.floor(2.6) == 2;

For negative numbers:

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

You can use toFixed method that also allows to specify the number of decimal numbers you want to show:

var num1 = new Number(3.141592);
var num2 = num1.toFixed(); // 3
var num3 = num1.toFixed(2); // 3.14
var num4 = num1.toFixed(10); // 3.1415920000

Just note that toFixed rounds the number:

var num1 = new Number(3.641592);
var num2 = num1.toFixed(); // 4

I use

function trunc(n){
   return n - n % 1;
}

because it works over the whole float range and should (not measured) be faster than

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

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