JavaScript section Summary

I. Lexical structure

1, JS inside the case-sensitive

2. Comments are divided into two categories://single-line comment/* multiline comment */

3, the literal quantity (direct quantity Literal)

12//numeric number

"hello" ' Hello '//string

True False//boolean type

Null//null type

/js/gi//regular

{x:1,y:2}//dictionary

[1,2,3,4]//array

4. Identifiers (variables) and reserved words

5, semicolon can be omitted but may cause problems, JS will automatically complete;

Ii. types, values, and variables

1. Primitive type: number, string and boolean, null null undefined not defined

2. Object type

3, class Array Function Date RegExp Error

4. Integrated garbage collection in JS parser

5, any value of JS can be converted to a Boolean value

Undefined

Null

0

-0

NaN

"" are converted to false

6. Packaging Objects

var s = "hello"; Primitive type (no METHOD)

S.len = 4; When a property or method of the original type is called (the original type has no properties and Methods)

Whenever a property of a string is referenced, a new string (s) is called to wrap the original type into an object

Subsequent calls to S.len are properties and methods that invoke the string object, and once the reference is complete, the newly created temporary object is destroyed

var n = s.len; This is undefined

Alert (n); A temporary object that is created when a property or method of a string Boolean number is Called. is the wrapper object display defines the wrapper object

var s = new String ("hello");

var s = "hello"; Two are Different.

7, = = and = = =

8. Type Conversion

var n = 17;

Alert (n.tostring (2)); Binary 10001

Alert (n.tostring (8)); 021

Alert (n.tostring (16)); 0x21

Alert (n.tostring (10));

Alert (n.tostring ());

9, toString () Value ()

var date = new Date (2011,1,3);

Date.valueof () returns the time represented by the number of milliseconds

10, JS is a dynamic type var n = 10; Type of variable is not determined during program run

11. Scope of variables

Scope and declaration of functions in advance

Variable declarations defined within functions are automatically advanced to the top of the function

12. Scope Chain Scope chain

In a function body that does not include a function, the scope chain has two objects, the first is the object of the custom function, the parameter and the layout variable, and the second is the global object

In a nested function body, There are at least three objects on the scope chain

When a function is defined, it holds a scope chain. When the function is called, it creates a new object to store its local variables, and adds the object to the saved scope chain, while creating a new "chain" that represents the scope of the function Call. For nested functions each time an external function is called, the inner function is redefined again. The scope chain is different each time an external function is Called.

13, Delete in eval void

third, the Object

1. Basic operation of object create set query Delete Test Enumetare

2. Object property Properties Writable enumerable lesson configuration (can be Deleted)

3. Object Characteristics of objects

Prototype of the object prototype

The string of the Object's class tag object type

Three ways to add new attributes//created extensions to the team Object's extended markup

4. Direct volume of objects

var empty = {};

var point = {x:0,y:0};

5. New Object creation

var o = new Object (); Empty objects are the same as {}

var a = new Array ();

6, object.create ()

var O1 = object.create ({x:1,y:2}); O1 inherited from Object prototype {x:1,y:2}

var O2 = Object.cteate (null); O2 cannot inherit any of the property methods

var O3 = Object.create (objec.prototype); Empty objects are the same as {}new object ()

7. operation of attributes as an object of an associative array

Object.property

object["property"] hash Map Dictionary associative array

8. Inheritance

Inherited object book is null or undefined

Book.subtitle.length will make an Error.

Workaround

var len = book&&book.subtitle&&book.subtitle.lenghth;

Delete Property

Delete Book,subtitle

Detection properties in Hasownpreperty () propertyisenumerable ()

var o = {x:1};

"x" in O

"toString" in O

Hasownpreperty (); Determine whether the property is your Own. Inheritance property returns False

propertyIsEnumerable () is only a property of its own and can be enumerated

Get all the properties

Object.keys ()

Object.getownpropertynames ()

9. Attribute getter and setter

var o = {

x:o,

y:1,

Set R (value) {value = this.r;},

Get R () {return this.x + this.y;}

};

X data properties, R accessor properties

10. Attribute characteristics Ecmascript5 old IE does not support the following usage

attribute of the data attribute: value of the writable writable

Enumerable enumerable

Configurable configurable

Accessor attribute properties: Get set

Enumerable enumerable

Configurable configurable

Return {value:1,writable:true,emunerable:true,configurable:true}

object.getownpropertydescriptor{{x:1},x}

Property returned undefined not found

Setting property properties Cannot modify inherited property attributes

Object.defineproperty ()

Set non-enumerable Properties

var o = {};

Object.defineproperty (o, "x", {

value:1,

writable:true,

emunerable:false,

Configurable:true

})

Set Read-only

Object.defineproperty (o, "x", {writable:false})

modifying multiple Property attributes

Object.defineproperties ()

11. Three properties of an object

Prototype Class extensible attribute

Querying the prototype of an object

Ecmascript5 in Object.getprototypeof (o1)

ECMASCRIPT3 in O1.constructor.prototype

Objects created by object direct amount or New object ()

A property that contains a constructor that is the constructor of the object ()

Constructor.prototype can be a real prototype.

P.isprototypeof () detects if the object P is a prototype of O

Gets the type string of the object

Object.prototype.toString.call (o1). Slice (8,-1)

12. Extensibility of objects

Whether the object can be newly added to the property

Object.preventextensions () Setting object is not extensible

Object.isextensible ()

Object.seal () In addition to setting the object to not be extensible, also set the property to not be configured

Object.freeze ()

In addition to setting the object to not be extensible, set the property to not configurable, and set the property to read-only,

Iv. functions

1. Function call, method call

function T () {}

T (); Function call this is the global object in strict mode is undefined

var o = {a:function () {}};

O.a () method Call this is the object that is currently being called

2. Constructor Call

var o = new Object (); var o= new Object;

o The This object is inside the prototype property that inherits from the constructor

var r = new O.M (), in which this is not O

3. The execution of the P184 function is used in the scope chain, which is created when the function definition is Defined.

The nested function f () is defined in the scope chain, where the variable scope is a local variable

Scope chain

Calling s () creates the execution environment (the calling Object) of the function s and places the object at the beginning of the List.

It then links the calling object of the function T to the next, and finally the global Object. Then look for the variable name from the beginning of the list

Call SS () SS () ==> t () ==> window

Name= "lwy";

function T () {

var name= "tlwy";

function S () {

var name= "slwy";

Console.log (name);

}

function SS () {

Console.log (name);

}

S ();

SS ();

}

T ();

Each time a function is called, a new scope chain is Generated. Including the new internal variables

JavaScript section Summary