JavaScript: Number Constructor
Number(arg)-
Convert arg to a number
Primitive Value
, return it .
// Number called as function, return a number primitive value console.log((typeof Number(3)) === "number");
new Number(arg)-
Convert arg to a number primitive value, return a number object that represent the number.
// Number called as constructor, returns a number object console.log((typeof (new Number(3))) === "object");
Convert to Number
| Argument Type | Result |
|---|---|
undefined | Return NaN. |
null | Return +0. |
true or false | Return 1 if argument is true. Return +0 if argument is false. |
| Number | Return argument (no conversion). |
| String | Return a number or NaN. |
| Symbol | Throw a TypeError exception. |
| Object | Return a number or NaN |
Special literal values of number.
// test converting special literal value to number primitive. // no change console.log(Number(Infinity) === Infinity); console.log(Number(-Infinity) === -Infinity); console.log(Number.isNaN(Number(NaN))); // changed console.log(Number.isNaN(Number(undefined))); console.log(Number(null) === 0); console.log(Number(true) === 1); console.log(Number(false) === 0); // all true
Convert string to number.
console.log(Number("0.03") === 0.03); // extra zero before or after is ok console.log(Number("00.03") === 0.03); console.log(Number("00.030") === 0.03); // extra space in front or back are ok console.log(Number(" 0.03 ") === 0.03); console.log(Number(" +0.03 ") === 0.03); console.log(Number(" -0.03 ") === -0.03); // cannot have space after sign console.log(Number.isNaN(Number("- 0.03 "))); // cannot have space between digits console.log(Number.isNaN(Number("1 000"))); // all true