Number() constructor

Syntax

new Number(value)
Number(value)

Parameters

value

The numeric value of the object being created.

Return value

When Number() is called as a function (without new), it returns value coerced to a number primitive. Specially, BigInts values are converted to numbers instead of throwing. If value is absent, it becomes 0.

When Number() is called as a constructor (with new), it uses the coercion process above and returns a wrapping Number object, which is not a primitive.

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

Browser compatibility

See also

• Polyfill of modern Number behavior (with support binary and octal literals) in core-js
• NaN
• Math
• BigInt