JavaScript Basics (First day)

The previous sentence: Mining the boundaries of knowledge, the finer, the depth and breadth of the higher, only the more cattle.

JS's performance has reached one-fifth of Java

(1) = = = = = = = = = = =??

Null = = undefined//true
' = = False//true
Summary = = not reliable, only with = = =

(2) do not use continue;

Low efficiency, Source: JavaScript language Essence 111 pages

(2) var a = {};

a.b= ' xx ';
a[' delete '] = ' yy '; The keywords don't matter.

(3) Delete deletion property
Global variables and local variables cannot be deleted???

var aaaa = 123;
Delete aaaa;
Console.log (AAAA); 123

WINDOW.AAAA = 123;
Delete window.aaaa;
Console.log (WINDOW.AAAA); Undefined

function A () {
var a= 123;
Delete A;
Console.log (a); 123
}a ();

Set as A=null; Pray to Heaven, wait for the garbage collection mechanism to be recycled.

Note: When declaring a variable with VAR, the property created is not configurable, that is, the delete operator cannot be removed

var name=1-No Delete

Sex= "Girl" to delete

THIS.AGE=22-To-remove

(4) typeof instanceof

typeof 2 = = = ' Number '//true
typeof new Number (2) = = = ' Number '//false
typeof ' 2 ' = = = ' String '//true
typeof new String (' 2 ') = = = ' String '//false
typeof true = = = ' Boolean '//true
typeof New Boolean (true) = = = ' Boolean '//false
typeof [] = = = ' object '//true
var a = function () {}; typeof a = = = ' function '; True

[] instanceof Object//true
2 instanceof Number//false
New Number (2) instanceof number//true

var a = function () {}
var B = function () {};
A.prototype = new B ();
New A () instanceof B; True

typeof can judge basic types and function
Instanceof can judge a custom object

Extended Object.prototype.toString.call ([]) = = = ' [Object Array] '; This is the best judgment.

(4) If statement
if (xxxx)? 6 cases of false

Null undefined NaN 0 "false

(4) for in
Traversing objects

Traversing a loose array

var a = new Array (10); a[2]=10; a[5]=10; for (var i in a) {Console.log (i);}

Performance, and did optimize the

var a = new Array (10000000);
a[2]=10;
a[5]=10;
var time1 = new Date (). GetTime ();
for (var i in a) {
Math.random () * MATH.RANDOM () * MATH.RANDOM () * Math.random ();
}
var time2 = new Date (). GetTime ();
for (var i=0; i<a.length; a++) {
Math.random () * MATH.RANDOM () * MATH.RANDOM () * Math.random ();
}
var time3 = new Date (). GetTime ();
Console.log (TIME2-TIME1); ~100ms
Console.log (time3-time2); ~200ms

(5) function literal and function declaration

var a = 2;
function A () {}
Console.log (typeof a); Function? Number?

Summarize:
The declaration of a variable is advanced to the top of the scope, and the assignment remains in place;
The declarative function is "in advance";
function expression only the variable "is advanced", the function is not "advanced";
The declaration of a function has a higher precedence than the declaration of a variable.
Assignments are overwritten according to the order of the front and back!

var a = function () {
Console.log (' AAA ');
}
function A () {
Console.log (' BBB ');
}
var B = function B () {} = = = function B () {}
A ();

(6) Function return value
var a = function (b,c) {
Console.log (b + ', ' +c);
}
Console.log (A ());

(7) This point
function A () {

var = self = this;

THIS.V = ' AAA ';
Function B () {
Console.log (this);
Console.log (THIS.V);
}
b ();
}
New A ();

(8) Arguments
function A (a,b,c,d) {
var args = [].slice.call (arguments);
}

(9) Apply Call
function A () {
Console.log (THIS.X+THIS.Y);
}
A.call ({x:100,y:100});

function C () {
THIS.M = function () {
Console.log (THIS.X+THIS.Y);
}
}
var c = new C ();
C.m.call ({x:100,y:100});

This is the redirect of this, forgive me, can't explain very accurate and easy to understand, can only practise more

(ten) Try catch throw key logic plus just fine
var a = ' AAA ';
try{
A = xxxx (); Methods that do not exist
}catch (e) {
Throw (new error (' Error '));
A = 0;
}
Console.log ("Go Go Go"); Is this the right way???

(11) Closures
for (var i=0; i<2; i++) {
}
Console.log (i);

function A () {
Only the method body has scope
}

var A;
Function C () {
var v = ' VVV ';
Function B () {
return {V:V};
};
A = B ();
}
C ();
Console.log (A.V); The method body is the scope, this everyone knows, the internal method body needs to give a cut out, let outside can access to.

(12) Callback

Function A (callback) {
Callback ();
}
A (function () {
Console.log (' AAA ');
});

(13) Self-executing function, also called self-tuning function

(function (a) {
Console.log (a);
}) (' AAA ');

(14) Regular
var regexp =//img
I case
M line break
G retrieves the first match without stopping, retrieving all

(prototype)
What is prototype?
function A () {
this.v= ' VVV ';
}
Console.log (A.prototype); The current object, the function is also an object,
Console.log (A.prototype.constructor); Current method
Console.log (a.prototype.constructor.__proto__ = = = a.__proto__); True
Prototype is the built-in property of the function, and __proto__ is the built-in property of the object, all of which look for the prototype chain

      //prototype usage scenarios?
      var b = {};
      //function B () {};
      //var b = function () {}
      b.prototype.bbb= ' BBB ';
      console.log (B.BBB);
      //console.log (new B (). bbb);//constructor

      //prototype how to play? (All of the following are bad usage)
      function A () {};
      a.prototype = function () {Console.log ("AAA")};
      console.log (new A.prototype ());

      //function A () {}
      //function B () {}
    & nbsp; //A.prototype = {aaa: ' AAA '};
      //b.prototype = A.prototype;
      //var aa1 = new A (),
      //AA2 = new A (),
       //BB1 = new B ();
      //aa1.prototype.aaa= ' xxx ';
      //console.log (AA2.AAA);
      //console.log (BB1.AAA);

function A () {}
Function B () {this.bbb= ' BBB '};
A.prototype = new B ();
Console.log (New A (). BBB);

-----4 It's actually like this.
Object.create ();

Last Word:!!! Only best technology practices can help!!!

JavaScript Basics (First day)