JS Simulation Object-Oriented Comprehensive Solution (2. Types and Assignment)_javascript skills

Type assignment is similar to the problem of variable passing.
Needless to say, basic data types are passed by value.

Copy code The code is as follows:

var a=5;
var b=a ;
b=3;
alert(a);//Hint 5
alert(b);//Hint 3

From this point of view, it is found that changing b does not will change a, because the values ​​of the variables are passed back and forth, and have nothing to do with the variables themselves.
Object type, pass-by address.

Copy code The code is as follows:

var a=new Object();
a.x =5;
var b=a;
b.x=3;
alert(a.x);//Prompt 3
alert(b.x);//Prompt 3

In this way, due to address passing, b is a and a is b, changing each other.
If it’s still unclear, here’s another example:

Copy the code The code is as follows:

var a=new Object();
a.x=5;
var b=a;
alert(b.x);//Prompt 5, b.x is a.x, both are 5
a.x=3 ;//Change a.x to change b.x, both are 3
alert(a.x);//Prompt 3
alert(b.x);//Prompt 3

However, the object type Assigning values ​​to each other's properties has nothing to do with the object type, but rather the type of its properties.
If the attribute is a basic data type, the value is passed, and if the attribute is an object type, the address is passed. For example, let’s make it simple:

Copy the code The code is as follows:

var a=new Object();
a.x=5; var b=new Object();
b.x=a.x; b.x=3;
alert(a.x); // Tip 5
alert(b.x); //Tip 3

What is assigned back and forth above is just the properties of two different objects. They are both isolated from each other and are basic data types. Therefore, they only transfer values ​​​​to each other and will not affect each other.

Copy code The code is as follows:

var a=new Object();
a.x =5;
var b=a.x;
b=3;
alert(a.x);/prompt/5
alert(b);//prompt 3

This is the same. The basic data type of b and the attribute x of the basic data type of a are assigned to each other. They also do not affect each other, but only transfer values ​​​​to each other.
However, if the properties of the object are also object types, then they are also passed by address.

Copy code The code is as follows:

var a=new Object();
a.x =new Object;
a.x.n=5;
var b=a.x;
alert(b.n);//Prompt 5
b.n=3;//This also changes the n of a.x
alert(a.x.n);//Prompt 3
alert(b.n);//Prompt 3

The attribute x of an object is defined as an Object object type. Therefore, when b is assigned the value a.x, they are interoperable. In fact, they are the same one and can influence and change each other.
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However, if I want to assign a value to an object type variable, I will just copy the attributes instead of reaching the realm of "you are me, I am you" and the noble character of "live and die together" . what to do?
There is no particularly good way, just use the following function.

Copy code The code is as follows:

var DeepCopy = function(destination, source)
{
for (var property in source)
　{
var copy = source[property];
if ( destination === copy ) continue;
if ( typeof copy === " object" )
　　{
destination[property] = DeepCopy(destination[property] || {}, copy);
　 }
　　　 else
　　;
　 }
}
return destination; 🎜>
The code is as follows:

var a=new Object;
a.x=5;
a.y=3;

var b=new Object; DeepCopy (b,a); alert(b.x);//Prompt 5 alert(b.y);//Prompt 3 b.x=8; alert(a.x);//Prompt 5

Look, modifying b.x does not affect a.x, right?
This DeepCopy is a good function.
The above implements the simulated "passing by value" of the object type
So how can we simulate the "passing by address" of the basic data type?
Just use Array object.

Copy code The code is as follows:

function change(a)
{
a[0]=5;
alert(a); // Tip 5
}
var x=[3];
alert(x); // Tip 3
change( x);
alert(x); // Tip 5

Assigning a [xx] is actually assigning an Array object with data. Here, an array containing one element is used to simulate address transfer. Because the array is an object type, it is passed by address when passing it.
Of course, you can also use properties of any object type to simulate.