Math.sign()

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The Math.sign() function returns either a positive or negative +/- 1, indicating the sign of a number passed into the argument. If the number passed into Math.sign() is 0, it will return a +/- 0. Note that if the number is positive, an explicit (+) will not be returned.

Syntax

Math.sign(x)

Parameters

x
A number. If this argument is not a number, it is implicitly converted to one.

Return value

A number representing the sign of the given argument:

  • If the argument is positive, returns 1.
  • If the argument is negative, returns -1.
  • If the argument is positive zero, returns 0.
  • If the argument is negative zero, returns -0.
  • 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).

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 aesthetic pseudo-representation:
    //
    // ( (x > 0) ? 1 : 0 )  // if x is positive, then positive one
    //          +           // else (because you can't be both - and +)
    // ( (x < 0) ? -1 : 0 ) // if x is negative, then negative 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 booleans to numbers.

Specifications

Specification Status Comment
ECMAScript 2015 (6th Edition, ECMA-262)
The definition of 'Math.sign' in that specification.
Standard Initial definition.
ECMAScript Latest Draft (ECMA-262)
The definition of 'Math.sign' in that specification.
Draft

Browser compatibility

Update compatibility data on GitHub
DesktopMobileServer
ChromeEdgeFirefoxInternet ExplorerOperaSafariAndroid webviewChrome for AndroidFirefox for AndroidOpera for AndroidSafari on iOSSamsung InternetNode.js
signChrome Full support 38Edge Full support 12Firefox Full support 25IE No support NoOpera Full support 25Safari Full support 9WebView Android Full support YesChrome Android Full support 38Firefox Android Full support 25Opera Android Full support YesSafari iOS Full support YesSamsung Internet Android Full support Yesnodejs Full support 0.12

Legend

Full support  
Full support
No support  
No support

See also