JavaScript Number isFinite() Method

What You’ll Learn

Number.isFinite() is a static method on Number (same API as MDN Number.isFinite). Call Number.isFinite(value) — not on a number instance. It returns true only for finite number values. This tutorial covers syntax, the difference from global isFinite(), five examples, and try-it labs.

Introduction

Division by zero, bad math, or missing data can produce Infinity or NaN. Before you format a value or send it to the UI, you often want to know: “Is this a real, finite number?”

Number.isFinite() answers that safely. Unlike the older global isFinite(), it does not convert strings or other types first — so Number.isFinite("25") is false.

This page is part of JavaScript Number Methods. Related checks include Number.isInteger() and Number.isNaN().

Understanding the isFinite() Method

Pass any value to Number.isFinite(value). You get true only when both of these are true:

• The type is "number" (not a string, object, or null).
• The number is finite — not Infinity, -Infinity, or NaN.

Everything else — including number-looking strings — returns false.

📝 Syntax

General form of the static method Number.isFinite:

Number.isFinite(value)

Parameters

• value (any) — the value to test for finiteness.

Return value

A boolean:

Exceptions

• None for normal calls — invalid types simply return false.

Common patterns

Number.isFinite(10 / 5);     // true
Number.isFinite(1 / 0);      // false
Number.isFinite(0 / 0);      // false
Number.isFinite("25");       // false
Number.isFinite(2e64);       // true
isFinite("25");              // true (global — coerces!)

Examples Gallery

Examples follow MDN patterns. Use View Output or Try It Yourself for each case.

Number.isFinite(10 / 5);  // true

true

Number.isFinite(1 / 0);  // false

false

Number.isFinite(0 / 0);  // false

false

Number.isFinite("25");  // false
// isFinite("25");      // true (global coerces)

false

Number.isFinite(2e64);  // true

true

🚀 Common Use Cases

• Guard UI formatters — only call toFixed / toPrecision on finite values.
• Validate math results — catch divide-by-zero before storing data.
• API payloads — reject Infinity / NaN that JSON cannot represent well.
• Form input — after Number(raw), confirm the result is finite.
• Safer than global isFinite — avoid accidental string/null coercion.
• Charts & gauges — skip plotting non-finite sensor readings.

📝 Notes

• This is a static method — use Number.isFinite(x) only.
• Does not coerce strings, booleans, null, or objects.
• Number objects (wrappers) are objects, so Number.isFinite(new Number(1)) is false.
• Global isFinite is older and coercing — prefer the Number static method in new code.
• Finite is not the same as integer — Number.isFinite(1.5) is true.
• For integer checks, use Number.isInteger().

💡 Best Practices