JavaScript variables can be converted to a new variable and another data type:
- By the use of a JavaScript function
- Automatically by JavaScript itself
Converting Numbers to Strings
The global method String() can convert numbers to strings.
It can be used on any type of numbers, literals, variables, or expressions:
Example
String(123) // returns a string from a number literal 123
String(100 + 23) // returns a string from a number from an expression
The Number method toString() does the same.
Example
(123).toString()
(100 + 23).toString()
In the chapter Number Methods, you will find more methods that can be used to convert numbers to strings:
| Method | Description |
|---|---|
| toExponential() | Returns a string, with a number rounded and written using exponential notation. |
| toFixed() | Returns a string, with a number rounded and written with a specified number of decimals. |
| toPrecision() | Returns a string, with a number written with a specified length |
Converting Booleans to Strings
The global method String() can convert booleans to strings.
String(true) // returns "true"
The Boolean method toString() does the same.
true.toString() // returns "true"
Converting Dates to Strings
The global method String() can convert dates to strings.
The Date method toString() does the same.
Example
In the chapter Date Methods, you will find more methods that can be used to convert dates to strings:
| Method | Description |
|---|---|
| getDate() | Get the day as a number (1-31) |
| getDay() | Get the weekday a number (0-6) |
| getFullYear() | Get the four digit year (yyyy) |
| getHours() | Get the hour (0-23) |
| getMilliseconds() | Get the milliseconds (0-999) |
| getMinutes() | Get the minutes (0-59) |
| getMonth() | Get the month (0-11) |
| getSeconds() | Get the seconds (0-59) |
| getTime() | Get the time (milliseconds since January 1, 1970) |
Converting Strings to Numbers
The global method Number() can convert strings to numbers.
Strings containing numbers (like "3.14") convert to numbers (like 3.14).
Empty strings convert to 0.
Anything else converts to NaN (Not a Number).
Number(" ") // returns 0
Number("") // returns 0
Number("99 88") // returns NaN
| Method | Description |
|---|---|
| parseFloat() | Parses a string and returns a floating point number |
| parseInt() | Parses a string and returns an integer |
The Unary + Operator
The unary + operator can be used to convert a variable to a number:
Example
var x = + y; // x is a number
If the variable cannot be converted, it will still become a number, but with the value NaN (Not a Number):
Example
var x = + y; // x is a number (NaN)
Converting Booleans to Numbers
The global method Number() can also convert booleans to numbers.
Number(true) // returns 1
Converting Dates to Numbers
The global method Number() can be used to convert dates to numbers.
Number(d) // returns 1404568027739
The date method getTime() does the same.
d.getTime() // returns 1404568027739
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