JavaScript: Number Constructor
Number(arg)- Convert arg to a number Primitive Value , return it .
new Number(arg)- Convert arg to a number primitive value, return a number object that represent the number.
// Number called as function, return a number primitive value console.log( ( typeof Number(3) ) === "number" ); // true
// Number called as constructor, returns a number object console.log( ( typeof (new Number(3)) ) === "object" ); // true
console.log( Number(3) === (new Number(3)) ); // false
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