files/en-us/web/javascript/reference/global_objects/isfinite/index.md

metadata

title: isFinite()
slug: Web/JavaScript/Reference/Global_Objects/isFinite
page-type: javascript-function
browser-compat: javascript.builtins.isFinite
sidebar: jssidebar

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()")}}

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

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")}}