Learn javaScript type conversion

JavaScript variables can be converted to a new variable:

Converting Javascript numbers to strings

Use the String( ) global method to convert numbers to string:

Code Example:

                    String(234)       // returns a string 
                   String(d)         // returns a string from a number variable d
String(10 + 5)  
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Converting Javascript booleans to strings

Use the String( ) global method to convert booleans to strings:

Code Example:

                    String(false)      // returns "false"
String(true)       // returns "true"

Converting Javascript dates to strings

Use the String( ) global method to convert dates to strings:

Code Example:

                    String(Date())  // returns "Thu month day year 12:12:12 GMT+numberarea (area day time)"


More methods that you can use:

Method Description
getDay() weekday (0-6)
getDate() day as a number (1-31)
getHours() hour (0-23)
getFullYear() four digit year (yyyy)
getMonth() month (0-11)
getTime() time (milliseconds since January 1, 1970)
getMinutes() minutes (0-59)
getSeconds() seconds (0-59)
getMilliseconds() milliseconds (0-999)

Converting Javascript strings to numbers

Use the Number( ) global method to convert strings to numbers:

Code Example:

                    Number(" ")       // returns 0
Number("5.11")    // returns 5.11
Number("")        // returns 0
Number("22 33")   // returns NaN

The Unary + Operator

Use the unary + operator to convert a variable to a number:

Code Example:

                    var a = "10";      // a is a string
var b = + a;      // b is a number
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Converting booleans to numbers

Use the Number( ) to convert booleans to numbers:

Code Example:

      Number(false)     // returns 0
Number(true)      // returns 1

Converting dates to numbers

Use the Number( ) to convert dates to numbers:

Code Example:

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

The date method getTime() does the same.

JavaScript Type Conversion Table

some results of diffrenet converting actions

Original Value Converted to Number Converted to String Converted to Boolean
0 0 "0" false
1 1 "1" true
true 1 "true" true
false 0 "false" false
"000" 0 "000" true
"ten" NaN "ten" true
" " 0 " " false
NaN NaN "NaN" false
function(){} NaN "function(){}" true
undefined NaN "undefined" false
null 0 "null" false
[ ] 0 " " true

JavaScript Data Types

there are 5 data types in Javascript:

  • number
  • string
  • boolean
  • function
  • object

the next data types can't contain values:

  • undefined
  • null

In Javascript there are 6 types of objects:

  • Date
  • String
  • Object
  • Array
  • Boolean
  • Number

String() converts to a String

Number() converts to a Number

Boolean() converts to a Boolean

Javascript typeof operator

to find data type of a variable use the typeof operator:

Code Example:

                    typeof 5.11                   // Returns "number"
                   typeof "Jake"                 // Returns "string"
                   typeof true                  // Returns "boolean"
typeof [2,3,4,5]              // Returns "object"
typeof {name:'Jake', age:12}  // Returns "object"
typeof NaN                    // Returns "number"
typeof myHat                  // Returns "undefined" *
typeof function () {}         // Returns "function"
typeof null                   // Returns "object"
typeof new Comment()             // Returns "object"
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Javascript constructor property

to find the a variable constructor function we use the constructor property:

Code Example:

                    (5.11).constructor                // Returns function Number()  {[native code]}
"Jake".constructor                // Returns function String()  {[native code]}
true.constructor                 // Returns function Boolean() {[native code]}
function () {}.constructor        // Returns function Function(){[native code]}
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If you want to check if the object is an Array function:

Code Example:

                    function isArray(myArray) {
  return myArray.constructor === Array;
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