JavaScript Basics (18) Type conversions

JavascriptType Conversions

Number () is converted to numbers, string () is converted to a string, and Boolean () is converted to a Boolean value.

JavaScript Data types

There are 5 different types of data in JavaScript:

• String
• Number
• Boolean
• Object
• function

3 Types of objects:

• Object
• Date
• Array

2 data types that do not contain any values:

• Null
• Undefined

typeof operator

You can use the typeof operator to view the data type of a JavaScript variable.

typeof"John"//returns a stringtypeof3.14//return numbertypeofNaN//return numbertypeof false                  //returns a Booleantypeof[1,2,3,4]//return Objecttypeof{name: ' John ', age:34}//return Objecttypeof NewDate ()//return Objecttypeof function() {}//return functiontypeofMyCar//returns undefined (if MyCar is not declared)typeof NULL                   //return Object

Please note:

• The data type of NaN is number
• The data type of the array is object
• Date data type is Object
• The data type of NULL is Object
• The data type of the undefined variable is undefined

If the object is a JavaScript Array or JavaScript Date, we cannot judge their type by typeof because it returns object.

Constructor property

The constructor property returns the constructor for all JavaScript variables.

"John". Constructor//returns the function String () {[native code]}(3.14). Constructor//return function number () {[native code]}false. constructor//return function Boolean () {[native code]}[1,2,3,4].constructor//returns the function Array () {[native code]}{name: ' John ', age:34}.constructor//return function Object () {[native code]}NewDate (). Constructor//return function Date () {[native code]}function() {}.constructor//return function functions () {[native code]}

You can use the constructor property to see if an object is an array (containing the string "Array"):

function IsArray (myArray) {    return myArray.constructor.toString (). IndexOf ("Array") >-1;}

You can use the constructor property to see if the object is a date (containing the string "date"):

function isDate (mydate) {    return myDate.constructor.toString (). IndexOf ("Date") >-1;}

JavaScript type Conversion

JavaScript variables can be converted to new variables or other data types:

• By using JavaScript functions
• Automatic conversion via JavaScript itself

Convert a number to a string

The global Method string () can convert a number to a string.

This method can be used for any type of number, letter, variable, expression:

String (x)         // converts the variable x to a string and returns a string (123)       // Converts the number 123 to a string and returns a string (100 + )  //  Converts a numeric expression to a string and returns

The number method toString () also has the same effect.

x.tostring ()(123). ToString () (+ +). ToString ()

In number, you can find more ways to convert numbers to strings:

Method	Description
Toexponential ()	Converts the value of an object to an exponential count method.
ToFixed ()	Converts a number to a string, the result of which has a specified number of digits after the decimal point.
Toprecision ()	Formats the number as the specified length.

Convert a Boolean value to a string

The global Method string () can convert a Boolean value to a string.

String (false)        //  return "false"string (true)         //  return "true"

The Boolean Method toString () also has the same effect.

false. ToString ()     //  returns "false"true. ToString ()      //  Returns "true"

Convert a date to a string

Date () returns a string.

Date ()      //  return Thu Jul 15:38:19 gmt+0200 (W. Europe Daylight Time)

The global method string () can convert a Date object to a string.

String (new Date ())      //  return Thu Jul 15:38:19 gmt+0200 (W. Europe Daylight Time)

The Date Method toString () also has the same effect.

New Date () obj.tostring ()    // return Thu Jul 15:38:19 gmt+0200 (W. Europe Daylight Time)

In the date method, you can see more about the functions of date conversions to strings:

Method	Description
GetDate ()	Returns the day of the one month (1 ~ 31) from the Date object.
GetDay ()	Returns the day of the week from a Date object (0 ~ 6).
getFullYear ()	Returns the year as a four-digit number from a Date object.
GetHours ()	Returns the hour (0 ~ 23) of the Date object.
Getmilliseconds ()	Returns the milliseconds (0 ~ 999) of the Date object.
Getminutes ()	Returns the minute (0 ~ 59) of the Date object.
GetMonth ()	Returns the month (0 ~ 11) from the Date object.
Getseconds ()	Returns the number of seconds (0 ~ 59) of the Date object.
GetTime ()	Returns the number of milliseconds since January 1, 1970.

JavaScript Basics (18) Type conversions