JS in this application

This is a keyword of JS, and the value of this will change as the function is used in different situations. But there is always a principle that this refers to the object that invokes the function.

1, pure function call.

function Test () {
    this.x = 1;
    alert (x);
}
Test ();

Actually this is the global variable. Look at the following example to understand the fact that this is the global object.

var x = 1;
function Test () {
    Alert (this.x);
}
Test (); //1

var x = 1;
function Test () {
this.x = 0;
}
Test ();
alert (x); //0 

2, as a method call, then this refers to this ancestor object.

function Test () {
    Alert (this.x);
}

var o = {};
o.x = 1;
O.M = test;
1

3. Called as a constructor function. The so-called constructor is the creation of a new object. At this point, this refers to this object.

function Test () {
    this.x = 1;
}
New test ();
alert (o.x); //1 

4. Apply Call

This points to the first parameter in apply.

var x = 0;
function Test () {
    Alert (this.x);
}

var o = {};
o.x = 1;
O.M = test;
0
O.m.apply (o); //1 

When apply has no parameters, it is represented as a global object. So the value is 0.

JS in this application