Number() constructor - JavaScript | MDN
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
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
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® 2027 Language Specification # sec-number-constructor |