JavaScript Advanced Extensions

-scope-related
1.
function func () {
if (1==1) {
var v= 123;
}
Console.log (v);
}
Func ()
A. error (java,c#) B. 123 (python, pair) c.undefined
= "javascript/python is scoped with function, non-parenthesis is scope
=" java,c# The brackets are scoped
2.
XO = ' root1 ';
function func () {
var xo = ' Root2 ';
function inner () {
console.log (xo);
}
Inner ();
}
Func ();
Scope chain
//root2
3.

xo = ' root1 ';
function func () {
var xo = ' Root2 ';
function inner () {
console.log (xo);
}
Return inner;
}
result = Func (),
Result (),
//scope chain was created before the function call, and when looking for a variable, find
//root2

4 based on the scope that was created at the Beginning.
XO = ' root1 ';
function func () {
var xo = ' Root2 ';
function inner () {
console.log (xo);
}
var xo = ' root3 '
return inner;
}
XO = "root4"
result = Func ();
Result ();

Root 3

5.
var xxxx;
Console.log (xxxx);


function Func () {
Console.log (xo);
var xo = ' 123 ';
Console.log (xo);
}
Func ()
Declaration in advance, JS Special
1. pre-compilation:
var xo; make xo=undefined;
2. implementation

6.
function Func (num) {
Console.log (num); function
num = 18;
Console.log (num); 18

function num () {
}
Console.log (num); 18
}
Func (666);

A. pre-compiling AO active object Activity objects
Compile the Parameters First:
Ao.num = undefined
Ao.num = 666
To recompile a variable:
If NUM is in the ao, no action is made
otherwise ao.num = undefined
Last Compile Function:
ao.num = function num () {
}

B. Implementation


7.

function Func (num) {
Console.log (num); function
function num () {
}
Console.log (num); function
num = 18;

Console.log (num); 18
}
Func (666);


Compile the Parameters First:
Ao.num = undefined
Ao.num = 666
To recompile a variable:
If NUM is in the ao, no action is made
otherwise ao.num = undefined
Last Compile Function:
ao.num = function num () {
}

8.
function Func () {
Console.log (xo);
var xo = 123;
}
Func ()

Compile:
Parameters:
AO is empty
Variable:
Ao.xo = undefined
Perform:

-functions and object-oriented Correlation
1.
function Func (arg) {
Console.log (this,arg);
}
Func (18);
Func.call (window,20);
Func.apply (window,[30]);


(function (arg) {
Console.log (this,arg);
}) (123)

When the function is executed, the default this is to refer to the Window object

function Func () {
Window.nn = ' Root ';
nn = ' root ';
This.nn = ' Root ';
}
Func ()
Console.log (nn);

=====>
A. Inside the function, the This variable is available by Default. By default, when you execute a function This=window
B. Use the name of the Function. call or function Name. apply can set the value in the

document.getElementById (' ID '). onclick = function () {
This
}

document.getElementById (' ID '). onclick.call (dom Object)


2. Is there a dictionary type in js?
Only objects are forged into dictionary form

var dict = {
Name: ' Alex ',
Age:18
}
Equivalent to
var dict = new Object (); # means creating an empty dictionary
Dict.name = ' Alex ';
Dict.age = 18;



function Foo (name) {
This. Name = Name
}

Foo (' Root ') # As a function, this is the default window
var dict1 = new Foo (' root1 ') # As a class, this is dict1 with the PY self
Foo.call (dict1, ' Root1 ')
var dict2 = new Foo (' root2 ') # As a class, this is the Dict2


====
function Foo (name) {
This. Name = name;
This. Func = function () {
Console.log (this. Name);
}
}
# as a function
Foo (' root1 ')
Window. Name
Window. Func ()

# as a class
obj = new Foo (' root2 ')
Obj. Name
Obj. Func ()

# Direct objects
Dict = {
Name: ' Root3 ',
Func:function () {
Console.log (this. Name);
}
}

# dict = new Object ();
# Dict. Name = ' Root3 ';
# Dict. Func = function () {
Console.log (this. Name);
}
Dict. Func ()
========================== "who called the function, this is who." function () Execution time default WINDOW. function ()


Who calls the function, this is who. function () Execution time default WINDOW. function ()
There is a this in every function
Name = ' 666 ';
var dict = {
Name: ' Root ',
age:18,
Func:function () {
This equals dict
Console.log (this. Name); Root

function Inner () {
Console.log (this. Name); 666
}
Window.inner ();
}
}

Dict. Func ();

============================
Who calls the function, this is who. function () Execution time default WINDOW. function ()
There is a this in every function
Variable Lookup order, scope chain
Name = ' 666 ';
var dict = {
Name: ' Root ',
age:18,
Func:function () {
This equals dict
Console.log (this. Name); Root
That equals Dict.
var = this;

function Inner () {
This=window
Console.log (that. Name); Root
}
Window.inner ();
}
}

Dict. Func ();

3. Prototypes

function Foo (name) {
This. Name = name;
}
Prototype
Foo.prototype = {
Func:function () {
Console.log (this. Name);
}
}

obj1 = new Foo (1)
Obj2 = new Foo (2)
obj3 = new Foo (3)

JavaScript Advanced Extensions