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 x 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.
    x = +x; // convert to a number
    if (x === 0 || isNaN(x)) {
      return Number(x);
    }
    return x > 0 ? 1 : -1;
  };
}

Specifications

Specification	Status	Comment
ECMAScript 2015 (6th Edition, ECMA-262) The definition of 'Math.sign' in that specification.	Standard	Initial definition.
ECMAScript 2017 Draft (ECMA-262) The definition of 'Math.sign' in that specification.	Draft

Browser compatibility

See also

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