Get the absolute value of a number in Javascript

Question

I want to get the absolute value of a number in JavaScript. That is, drop the sign. I know mathematically I can do this by squaring the number then taking the square root, but I also know that this is horribly inefficient.

x = -25
x = x * x 
x = Math.sqrt(x)
console.log(x)

Is there a way in JavaScript to simply drop the sign of a number that is more efficient than the mathematical approach?

Answer 1

You mean like getting the absolute value of a number? The Math.abs javascript function is designed exactly for this purpose.

var x = -25;
x = Math.abs(x); // x would now be 25 
console.log(x);

Here are some test cases from the documentation:

Math.abs('-1');     // 1
Math.abs(-2);       // 2
Math.abs(null);     // 0
Math.abs("string"); // NaN
Math.abs();         // NaN

Answer 2

Here is a fast way to obtain the absolute value of a number. It's applicable on every language:

x = -25;
console.log((x ^ (x >> 31)) - (x >> 31));

Answer 3

If you want to see how JavaScript implements this feature under the hood you can check out this post.

Blog Post

Here is the implementation based on the chromium source code.

function MathAbs(x) {
  x = +x;
  return (x > 0) ? x : 0 - x;
}

console.log(MathAbs(-25));

Answer 4

I think you are looking for Math.abs(x)

https://developer.mozilla.org/en/JavaScript/Reference/Global_Objects/Math/abs

Answer 5

Alternative solution

Math.max(x,-x)

let abs = x => Math.max(x,-x);

console.log( abs(24), abs(-24) );

Also the Rick answer can be shorted to x>0 ? x : -x

Answer 6

to simply drop the sign of a number

var x = -25;
+`${x}`.replace('-', '');