JavaScript Advanced Knowledge Analysis--instantiation

The code information comes from http://ejohn.org/apps/learn/.

What has new been doing?

function Ninja () {   this. Name = "Ninja";}    var ninjaa ="Undefined,ninja is not instantiated" );   var New  = = "Ninja", "true, existence of name attribute in instantiation")

The new operation of a function is instantiated.

The process of the above code is to create a temporary object, inherit the Ninja.prototype object, execute the function ninja, and initially set the context this to a temporary object. Returns the temporary object without a return statement.

Our context this points to the instantiated object

functionNinja () { This. swung =false; //should return True   This. Swingsword =function(){      This. swung =! This. Swung; return  This. Swung; }; }  varNinja =NewNinja (); Console.log (Ninja.swingsword (),"Invoke Instance Object method" ); Console.log (Ninja.swung,"Referencing instance object Properties" ); varNinjab =NewNinja (); Console.log (!ninjab.swung, "determines that the property referenced by this is a property of the instantiated object, and that the instantiated object does not affect each other.");

Exercise: Add a method that can give ninja a Name property

function Ninja (name) {   // complement }  varnew Ninja ("John"= = "John", "Name property is set at initialization" );  Ninja.changename ("Bob"= = "Bob", "Name Value modified successfully");

Add a new property and method to the instantiated object

function Ninja (name) {   thisfunction(name) {     this. Name = name ;  }   this. ChangeName (name)}  varnew Ninja ("John"= = " John "," The name attribute is set when initializing " );  Ninja.changename ("Bob"= = "Bob", "Name Value modified successfully");

What happens when new is not used?

function User (First, last) {   this. Name = First + "" + Last ;}    var user = User ("John", "Resig"typeof user = = "undefined", "because there is no new, so the user makes a general function call, no return value");

function User (First, last) {   this. Name = First + "" + Last ;}    = "Resig"var user = User ("John", name);   = = "John resig", "Global attribute is overwritten");

When there is no new, it is actually a general function call, followed by the nature of the function call.

Ensure that object instantiation is still used in case of error

function User (First, last) {   if (!) (  This instanceof User))      return New User (First, last);    this. Name = First + "" + Last ;}   var name = "Resig"var user = User ("John", name);  " Even if you do not use new, you can stillproperly instantiate "= =" Resig "," instantiation of the property is normal ");

By judging this is not an instantiated object of the constructor user, it is re-instantiated, a technique that can be instantiated without using new.

Exercise: Is there a more genetically-structured way to do the same thing?

function User (First, last) {   if (!) (  This instanceof  ___) )      return New User (First, last);    this. Name = First + "" + Last ;}   var name = "Resig"var user = User ("John", name);  " Even if you do not use new, you can stillproperly instantiate "= =" Resig "," instantiation of the property is normal ");

Implemented with Arguments.callee

function User (First, last) {   if (!) (  This instanceof  ___) )      return New User (First, last);    this. Name = First + "" + Last ;}   var name = "Resig"var user = User ("John", name);  " Even if you do not use new, you can stillproperly instantiate "= =" Resig "," instantiation of the property is normal ");

Arguments.callee refers to the function itself.

JavaScript Advanced Knowledge Analysis--instantiation