isNumber()

isNumber(value): value is number

Checks if a value is a number.

note

Includes NaN and Infinity. Use Number.isFinite() for finite numbers only.

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Parameters

value: unknown

The value to check.

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Returns: value is number

true if the value is a number, false otherwise.

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See Also

isFinite

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Since

1.0.0

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Example

isNumber(42);       // => true
isNumber(3.14);     // => true
isNumber(NaN);      // => true
isNumber(Infinity); // => true
isNumber('42');     // => false

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How it works?

Type guard that checks if a value is a number (excluding NaN).

Type Narrowing

Common Checks

Value	Result
123	true
0	true
-1.5	true
Infinity	true
NaN	false
'123'	false
new Number(123)	false (boxed)

Note

Unlike typeof x === 'number', this guard excludes NaN for safer number handling.

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Use Cases

Validate numeric inputs 📌

Ensure a value is a number before calculations. Essential for form handling and data validation.

#validate#number#numeric#inputs#calculations#forms

if (isNumber(input) && !isNaN(input)) {
  const total = input + tax;
}

Filter valid numbers from mixed data

Extract numeric values from arrays containing mixed types.

#filter#numbers#mixed#types#extraction#validation

const values = [1, "two", 3, null, 4];
const numbers = values.filter(isNumber);
// numbers: number[] = [1, 3, 4]