·         Converting Strings to Numbers

·         Converting Numbers to Strings

·         Converting Dates to Numbers

·         Converting Numbers to Dates

·         Converting Booleans to Numbers

·         Converting Numbers to Booleans

JavaScript Type Conversion

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 Strings to Numbers

The global method Number() converts a variable (or a value) into a number.

A numeric string (like "3.14") converts to a number (like 3.14).

An empty string (like "") converts to 0.

A non numeric string (like "John") converts to NaN (Not a Number).

Examples

These will convert:

Number("3.14")
Number(Math.PI)
Number(" ")
Number("")

These will not convert:

Number("99 88")
Number("John")

 

Number Methods

In the chapter Number Methods, you will find more methods that can be used to convert strings to numbers:

Method	Description
Number()	Returns a number, converted from its argument
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

let y = "5";      // y is a string
let 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

let y = "John";   // y is a string
let x = + y;      // x is a number (NaN)

 

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(x)         // returns a string from a number variable x
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

x.toString()
(123).toString()
(100 + 23).toString()

 

More Methods

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 Dates to Numbers

The global method Number() can be used to convert dates to numbers.

d = new Date();
Number(d)          // returns 1404568027739

The date method getTime() does the same.

d = new Date();
d.getTime()        // returns 1404568027739

Converting Dates to Strings

The global method String() can convert dates to strings.

String(Date())  // returns "Thu Jul 17 2014 15:38:19 GMT+0200 (W. Europe Daylight Time)"

The Date method toString() does the same.

Example

Date().toString()  // returns "Thu Jul 17 2014 15:38:19 GMT+0200 (W. Europe Daylight Time)"

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)

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