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 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.

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

Examples

undefined

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

See also