JavaScript common data types and data conversion

First, the original data type: string, number, Boolean, null, Undefined, object. (Simple use (typeof xx) to judge)

1) Basic Data type:

A) string (string)

Data base types (arguments) and reference types

1. Define a string of basic data type var s = "xiao.ming";

2. Define a reference type for the basic data var s = new String ("xiao.ming");

Defines the property of a data type S.name = "Ming";

Defines a method that has a data type s.age = function () {return 20;};

At the time of reference: alert (box);
Alert (box.substring (2)); System built-in objects, all valid
alert (box.name); Custom methods: 1 invalid, 2 valid
Alert (Box.age ()); Custom methods: 1 invalid, 2 valid

Common methods of basic data types

Alert (S.chatat (1)); I

Alert (S.indexof ("I"));//2;//Search from the beginning of the T position
Alert (S.lastindexof (' t '));//3;//search for the position of T from the tail

String also has a method of manipulating strings, contact (' is ', ' teacher '), slice 1 to 2 characters, substr (2,4) from the second
Start selecting four characters, substring 1 to 2;

Difference
S.slice (-2); method of calculation; Total string length 2 = 6; so S.slice ( -2) = = S.slice (6);
S.substring (-2), if it is a negative number. Return all strings

2) Number

var n = 100;

eg: static type
alert (N.max_value); Undefined
Alert (number. max_value); static type of//number

Common methods for Number objects
Alert (box.tostring ()); Box is a number type and is now a string type;
Alert (box.tolocalesring ()); Localization
Alert (box.tofixed (2)); The decimal point is reserved two bits and rounded

Note: Other static methods and basic types of methods you can find the mother.

3) Boolean

Boolean has only two logical values: true| | False

var x = "HI";

var Xasboolean = Boolean (HI);

When this is defined, you can use the following judgment

if (x) {alert ("value is true!");};

4) null and undefined

var x = "";//null, and null is the keyword

var y;//no type;

Eg: A family of three people are in the house at this time: .... Then 2 went out, at this time for this room, 2 bit null, if 4, is undefined, is not there;

5) Composite data type Object

Here is a simple understanding of object, it has a lot of knowledge.

The simple understanding of object is: unordered collection of Members

var person={firstname: "Bill", LastName: "Gates", id:5566};

|| var person = new Object;p erson={firstname: "Bill", LastName: "Gates", id:5566};

Read person value

var name = Person.firstname | | var name = person["FirstName"];

Second, data conversion

Tonumber: Convert to Number type
ToString: Convert to String type
ToBoolean: Convert to Boolean
Toobject: Convert to type Object
Toprimitive: Convert to original type

JavaScript common data types and data conversions