Math.sign()

The Math.sign() function returns the sign of a number, indicating whether the number is positive, negative or zero.

Syntax

Math.sign(x)

Parameters

x

A number.

Return value

A number representing the sign of the given argument. If the argument is a positive number, negative number, positive zero or negative zero, the function will return 1, -1, 0 or -0 respectively. Otherwise, NaN is returned.

Description

Because sign() is a static method of Math, you always use it as Math.sign(), rather than as a method of a Math object you created (Math is not a constructor).

This function has 5 kinds of return values, 1, -1, 0, -0, NaN, which represent "positive number", "negative number", "positive zero", "negative zero" and NaN respectively.

The argument passed to this function will be converted to number type implicitly.

Examples

Using Math.sign()

Math.sign(3);     //  1
Math.sign(-3);    // -1
Math.sign('-3');  // -1
Math.sign(0);     //  0
Math.sign(-0);    // -0
Math.sign(NaN);   // NaN
Math.sign('foo'); // NaN
Math.sign();      // NaN

Polyfill

if (!Math.sign) {
  Math.sign = function(x) {
    // If x is NaN, the result is NaN.
    // If x is -0, the result is -0.
    // If x is +0, the result is +0.
    // If x is negative and not -0, the result is -1.
    // If x is positive and not +0, the result is +1.
    return ((x > 0) - (x < 0)) || +x;
    // A more aesthetical persuado-representation is shown below
    //
    // ( (x > 0) ? 0 : 1 )  // if x is negative then negative one
    //          +           // else (because you cant be both - and +)
    // ( (x < 0) ? 0 : -1 ) // if x is positive then positive one
    //         ||           // if x is 0, -0, or NaN, or not a number,
    //         +x           // Then the result will be x, (or) if x is
    //                      // not a number, then x converts to number
  };
}

In the above polyfill, no extra type-coercing is needed to make (x > 0) or (x < 0) numbers because subtracting them from each other forces a type conversion from boolean to numbers.

Specifications

Browser compatibility

The compatibility table in this page is generated from structured data. If you'd like to contribute to the data, please check out https://github.com/mdn/browser-compat-data and send us a pull request.

See also

• Math.abs()
• Math.ceil()
• Math.floor()
• Math.round()
• Math.trunc()