Dive Into JavaScript

The JavaScript isFinite Function

The JavaScript isFinite global function determines whether a value is a finite number.

All numbers in JavaScript are 64-bit floating point numbers which yields a range of 5e-324 (Number.MIN_VALUE) to 1.7976931348623157e+308 (Number.MAX_VALUE). Any number that exceeds the lower or upper limit of the floating point numbers is considered infinite. The isFinite function can be used to determine whether a given value is within the allowed range for a floating point number.

The isFinite function tries to convert the value to a number. If the result is NaN, positive infinity (Infinity) or negative infinity (-Infinity), isFinite returns false. Otherwise, it returns true.

Syntax

var is_finite = isFinite(value);

Parameters

value

The value being evaluated

Examples

isFinite(42); // true
isFinite(Math.sqrt(-4)); // false
isFinite("I am not a number, I am a free man."); // false

See also

• The Infinity property
• The NaN property
• The Number object