js prototype chain principle diagram explanation_javascript skills-JS Tutorial-php.cn

js prototype chain principle diagram explanation_javascript skills

WBOY

Release： 2016-05-16 17:51:59

Original

1208 people have browsed it

The inventor of ECMAscript designed this linked list in order to simplify the language while maintaining inherited properties. .
Have you ever learned about linked lists in data structures? There is a position in the linked list that is equivalent to a pointer, pointing to the next structure.

So the same goes for __proto__. Whenever you define a prototype, it is equivalent to pointing the __proto__ of the instance to a structure. Then the pointed structure is called the instance. prototype.

The text is a bit convoluted, look at the pictures to speak

Copy the code The code is as follows:

 
var foo = { 
x: 10, 
y: 20 
}; 

Figure 1. A basic object with a prototype.

When I do not specify __proto__, foo will also reserve such an attribute.

If there is a clear pointer, then the linked list will be linked. La.

Obviously, b and c in the figure below share the attributes and methods of a, and at the same time have their own private attributes.

__proto__ also has pointing by default. It points to the highest-level object.prototype, and the __proto__ of object.prototype is empty.

Copy code The code is as follows:

 
var a = { 
x: 10, 
calculate: function (z) { 
return this.x this.y z 
} 
}; 
var b = { 
y: 20, 
__proto__: a 
}; 

var c = { 
y: 30, 
__proto__: a 
}; 

// call the inherited method 
b.calculate( 30); // 60 

Figure 2. A prototype chain.

Understand the nature of the attribute link pointer __proto__. . Let’s understand constructor again.

When a prototype is defined, a prototype object will be constructed, and this prototype object is stored in the prototype method of the function that constructs the prototype.

Copy the code The code is as follows:

 
function Foo(y){ 
this.y = y ; 
} 

Foo. prototype.x = 10; 

Foo.prototype.calculate = function(z){ 
return this.x this.y z; 
}; 

var b = new Foo (20); 

alert(b.calculate(30)); 

Figure 3. A constructor and objects relationship.