Number() constructor

The Number() constructor creates Number objects. When called as a function, it returns primitive values of type Number.

Syntax

js

new Number(value)
Number(value)

Note: Number() can be called with or without new, but with different effects. See Return value.

Parameters

value

The numeric value of the object being created.

Return value

When Number is called as a constructor (with new), it creates a Number object, which is not a primitive.

When Number is called as a function, it coerces the parameter to a number primitive. BigInts are converted to numbers. If the value can't be converted, it returns NaN.

Warning: You should rarely find yourself using Number as a constructor.

Examples

Creating Number objects

js

const a = new Number("123"); // a === 123 is false
const b = Number("123"); // b === 123 is true
a instanceof Number; // is true
b instanceof Number; // is false
typeof a; // "object"
typeof b; // "number"

Using Number() to convert a BigInt to a number

Number() is the only case where a BigInt can be converted to a number without throwing, because it's very explicit.

js

+1n; // TypeError: Cannot convert a BigInt value to a number
0 + 1n; // TypeError: Cannot mix BigInt and other types, use explicit conversions

js

Number(1n); // 1

Note that this may result in loss of precision, if the BigInt is too large to be safely represented.

js

BigInt(Number(2n ** 54n + 1n)) === 2n ** 54n + 1n; // false

Specifications

Specification
ECMAScript Language Specification
# sec-number-constructor

Browser compatibility

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See also