isFinite()

The isFinite() function determines whether a value is finite, first converting the value to a number if necessary. A finite number is one that's not {{jsxref("NaN")}} or ±{{jsxref("Infinity")}}. Because coercion inside the isFinite() function can be surprising, you may prefer to use {{jsxref("Number.isFinite()")}}.

{{InteractiveExample("JavaScript Demo: isFinite()")}}

```js interactive-example function div(x) { if (isFinite(1000 / x)) { return "Number is NOT Infinity."; } return "Number is Infinity!"; }

console.log(div(0)); // Expected output: "Number is Infinity!""

console.log(div(1)); // Expected output: "Number is NOT Infinity."

## Syntax

```js-nolint
isFinite(value)

Parameters#

• value
• : The value to be tested.

Return value#

false if the given value is {{jsxref("NaN")}}, {{jsxref("Infinity")}}, or -Infinity after being converted to a number; otherwise, true.

Description#

isFinite() is a function property of the global object.

When the argument to the isFinite() function is not of type Number, the value is first coerced to a number, and the resulting value is then compared against NaN and ±Infinity. This is as confusing as the behavior of {{jsxref("isNaN")}} — for example, isFinite("1") is true.

{{jsxref("Number.isFinite()")}} is a more reliable way to test whether a value is a finite number value, because it returns false for any non-number input.

Examples#

Using isFinite()#

isFinite(Infinity); // false
isFinite(NaN); // false
isFinite(-Infinity); // false

isFinite(0); // true
isFinite(2e64); // true
isFinite(910); // true

// Would've been false with the more robust Number.isFinite():
isFinite(null); // true
isFinite("0"); // true

Specifications#

{{Specifications}}

Browser compatibility#

{{Compat}}

See also#

• {{jsxref("Number.isFinite()")}}
• {{jsxref("Number.NaN")}}
• {{jsxref("Number.POSITIVE_INFINITY")}}
• {{jsxref("Number.NEGATIVE_INFINITY")}}