javascript高级知识分析——实例化

function Ninja(){ 
  this.name = "Ninja"; 
} 
 
var ninjaA = Ninja(); 
console.log( ninjaA, "undefined,ninja并不是实例化" ); 
 
var ninjaB = new Ninja(); 
console.log( ninjaB.name == "Ninja", "true,在实例化里存在name属性" )

function Ninja(){ 
  this.swung = false; 
   
  // Should return true 
  this.swingSword = function(){ 
    this.swung = !this.swung; 
    return this.swung; 
  }; 
} 
 
var ninja = new Ninja(); 
console.log( ninja.swingSword(), "调用实例对象方法" ); 
console.log( ninja.swung, "引用实例对象属性" ); 
 
var ninjaB = new Ninja(); 
console.log( !ninjaB.swung, "确定this引用的属性是实例化对象的属性，实例化对象彼此不影响." );

function Ninja(name){ 
  //补足
} 
 
var ninja = new Ninja("John"); 
console.log( ninja.name == "John", "在初始化时name属性就被设置" ); 
 
ninja.changeName("Bob"); 
console.log( ninja.name == "Bob", "name值成功修改" );

function Ninja(name){ 
  this.changeName = function(name){
     this.name = name;
  }
  this.changeName(name)
} 
 
var ninja = new Ninja("John"); 
console.log( ninja.name == "John", "在初始化时name属性就被设置" ); 
 
ninja.changeName("Bob"); 
console.log( ninja.name == "Bob", "name值成功修改" );

function User(first, last){ 
  this.name = first + " " + last; 
} 
 
var user = User("John", "Resig"); 
console.log( typeof user == "undefined", "因为没有new，所以User作一般函数调用，没有返回值" );

function User(first, last){ 
  this.name = first + " " + last; 
} 
 
window.name = "Resig"; 
var user = User("John", name); 
 
console.log( name == "John Resig", "全局属性被覆盖" );

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); 
 
console.log( user, "即使没有使用new,仍然可以正确实例化" ); 
console.log( name == "Resig", "实例化属性正常" );

function User(first, last){ 
  if ( !(this instanceof ___) ) 
    return new User(first, last); 
  this.name = first + " " + last; 
} 
 
var name = "Resig"; 
var user = User("John", name); 
 
console.log( user, "即使没有使用new,仍然可以正确实例化" ); 
console.log( name == "Resig", "实例化属性正常" );

function User(first, last){ 
  if ( !(this instanceof ___) ) 
    return new User(first, last); 
  this.name = first + " " + last; 
} 
 
var name = "Resig"; 
var user = User("John", name); 
 
console.log( user, "即使没有使用new,仍然可以正确实例化" ); 
console.log( name == "Resig", "实例化属性正常" );