Math.fround()
The Math.fround()
static method returns the nearest 32-bit single precision float representation of a number.
Try it
Syntax
js
Math.fround(doubleFloat)
Parameters
doubleFloat
-
A number.
Return value
The nearest 32-bit single precision float representation of x
.
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:
js
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:
js
Math.fround(1.337); // 1.3370000123977661
Math.fround(1.337) === 1.337; // false
is too big for a 32-bit float, so Infinity
is returned:
js
2 ** 150; // 1.42724769270596e+45
Math.fround(2 ** 150); // Infinity
Specifications
Specification |
---|
ECMAScript Language Specification # sec-math.fround |
Browser compatibility
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