Some JavaScript quiz

ArticleDirectory

• A. X = A ={}, in-depth understanding of the value assignment expression
• Abbreviation of If statement
• & | The calculated value
• Object Construction
• Prototype details
• Create an object and keep the prototype chain

A. X = A ={}, in-depth understanding of the value assignment expression

 

Code

  VaR  O  =  {X:  1  };
  VaR  A =  O;

A. x  =  A  =  {Name:  100  };

Console. Log (A. X );  //  Undefined  
  Console. Log (O. X );  //  {Name: 100}  
  
  // A. X = A = {Name: 100 };  
//  Equivalent to A. X = (a = {Name: 100 });  
//  Calculate the reference of A. X, and then calculate the return value of (a = {Name: 100 })  
 

 

Abbreviation of If statement

 

  VaR  Condition  =     True  , Numb =     0  ;
  If  (Condition ){
Alert (  '  Rain-man  '  )
}
  If  (Condition ){
Numb  =     1     +    2  ;
}
 

Equivalent

 

  VaR  Condition  =     True  , Numb  =     0  ;
Condition  && Alert (  '  Rain-man  '  );
Condition  &&  (Numb  =     1     +     2  );
 

& | The calculated value

 

  (  True     &&     222  );  //  222  
  !!  (  True     &&    222  );  //  True  
  (  False     &&     222  );  //  False  
 

 

   code highlighting produced by actipro codehighlighter (freeware) 
 http://www.CodeHighlighter.com/
 -->  (  false    ||    222  );  ///   222   
   !!   (  false    ||    222  );  ///   true   
  

!! Variable returns a Boolean value equal to the original value.

Object Construction

 

Code

  Function  Object () {[native code]}
Object. Prototype  =  {
Constructor:  Function  Object () {[native code]},
Hasownproperty:  Function  Hasownproperty () {[native code]},
Isprototypeof:  Function Isprototypeof () {[native code]},
Propertyisenumerable:  Function  Propertyisenumerable () {[native code]},
Tolocalestring:  Function  Tolocalestring () {[native code]},
Tostring:  Function  Tostring () {[native code]},
Valueof:  Function  Valueof () {[native code]}
};

Object. Prototype. Constructor  ===  Object;  // True  
 

Prototype details

 

  VaR  A  =     Function  (){
  This  . Name  =     '  Rain-man '  ;
};
A. Prototype  =  {
Name:  '  Cnblogs  '  
};
  VaR  O  =     New  A ();
Console. Log (O. Name );  //  'Rain-man'  
 

Create an object and keep the prototype chain

 

Code

  VaR  O  =     Function  (OBJ ){
  Function  T (){}
T. Prototype  =  OBJ;
  Return    New  T ();
};

  VaR  OBJ  =  {Name:  '  OBJ  '  , Age:  0  },
Obj1  =  O (OBJ ),
Obj2  =  O (obj1 );

  // Change one location of the prototype chain and all prototype chains will change  
  OBJ. Name  =     '  Superclass  '  ;
Console. Log (obj1.name );  //  'Superclass'  
  Console. Log (obj2.name );  //  'Superclass'  
 
  //  Each layer can be processed separately.  
  Obj1.name  =     100  ;
Console. Log (obj1.name );  //  100  
  Delete  Obj1.name;  //  Violence and leakage prototype chain  
 Console. Log (obj1.name );  //  'Superclass'