Converting Variables to Numbers
There are 3 JavaScript methods that can be used to convert variables to numbers:
- The
Number()method - The
parseInt()method - The
parseFloat()method
These methods are not number methods, but global JavaScript methods.
Global JavaScript Methods
JavaScript global methods can be used on all JavaScript data types.
These are the most relevant methods, when working with numbers:
| Method | Description |
|---|---|
| Number() | Returns a number, converted from its argument. |
| parseFloat() | Parses its argument and returns a floating point number |
| parseInt() | Parses its argument and returns an integer |
The Number() Method
Number() can be used to convert JavaScript variables to numbers:
Example
Number(false); // returns 0
Number("10"); // returns 10
Number(" 10"); // returns 10
Number("10 "); // returns 10
Number(" 10 "); // returns 10
Number("10.33"); // returns 10.33
Number("10,33"); // returns NaN
Number("10 33"); // returns NaN
Number("John"); // returns NaN
If the number cannot be converted, NaN (Not a Number) is returned.
The Number() Method Used on Dates
Number() can also convert a date to a number:
Example
The Number() method above returns the number of milliseconds since 1.1.1970.
The parseInt() Method
parseInt() parses a string and returns a whole number. Spaces are allowed. Only the first number is returned:
Example
parseInt("-10.33"); // returns -10
parseInt("10"); // returns 10
parseInt("10.33"); // returns 10
parseInt("10 20 30"); // returns 10
parseInt("10 years"); // returns 10
parseInt("years 10"); // returns NaN
If the number cannot be converted, NaN (Not a Number) is returned.
The parseFloat() Method
parseFloat() parses a string and returns a number. Spaces are allowed. Only the first number is returned:
Example
parseFloat("10.33"); // returns 10.33
parseFloat("10 20 30"); // returns 10
parseFloat("10 years"); // returns 10
parseFloat("years 10"); // returns NaN
NaN (Not a Number) is returned. Practice Excercise Practice now