Number() constructor

The Number() constructor creates a Number object. When called instead as a function, it performs type conversion to a primitive number, which is usually more useful.

Syntax

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

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.

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

Number(1n); // 1

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

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

Specifications

Specification
ECMAScript Language Specification # sec-number-constructor

Browser compatibility

BCD tables only load in the browser