The Math.fround() function returns the nearest 32-bit single precision float representation of a Number.

Syntax

var singleFloat = Math.fround(doubleFloat);

Parameters

doubleFloat
A Number. If the parameter is of a different type, it will get converted to a number or to NaN if it cannot be converted.

Return value

The nearest 32-bit single precision float representation of the given number.

Description

JavaScript uses 64-bit double floating-point numbers internally, which offer a very high precision. However, sometimes you may be working with 32-bit floating-point numbers, for example if you are reading values from a Float32Array. This can create confusion: Checking a 64-bit float and a 32-bit float for equality may fail even though the numbers are seemingly identical.

To solve this, Math.fround() can be used to cast the 64-bit float to a 32-bit float. Internally, JavaScript continues to treat the number as a 64-bit float, it just performs a "round to even" on the 23rd bit of the mantissa, and sets all following mantissa bits to 0. If the number is outside the range of a 32-bit float, Infinity or -Infinity is returned.

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

Examples

Using Math.fround()

The number 1.5 can be precisely represented in the binary numeral system, and is identical in 32-bit and 64-bit:

Math.fround(1.5); // 1.5
Math.fround(1.5) === 1.5; // true

However, the number 1.337 cannot be precisely represented in the binary numeral system, so it differs in 32-bit and 64-bit:

Math.fround(1.337); // 1.3370000123977661
Math.fround(1.337) === 1.337; // false

21502^150 is too big for a 32-bit float, so Infinity is returned:

2 ** 150; // 1.42724769270596e+45
Math.fround(2 ** 150); // Infinity

If the parameter cannot be converted to a number, or it is not-a-number (NaN), Math.fround() will return NaN:

Math.fround('abc'); // NaN
Math.fround(NaN); // NaN

Polyfill

This can be emulated with the following function, if Float32Array are supported:

Math.fround = Math.fround || (function (array) {
  return function(x) {
    return array[0] = x, array[0];
  };
})(new Float32Array(1));

Specifications

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

Browser compatibility

FeatureChromeEdgeFirefoxInternet ExplorerOperaSafari
Basic support38 Yes26 No258
FeatureAndroid webviewChrome for AndroidEdge mobileFirefox for AndroidOpera AndroidiOS SafariSamsung Internet
Basic support Yes Yes Yes26 Yes8 Yes

See also

Document Tags and Contributors

 Last updated by: schlagi123,