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This detailed introduction to the javascript operating mechanism_Basic knowledge
This detailed introduction to the javascript operating mechanism_Basic knowledge
This is an important keyword in object-oriented languages. Understanding and mastering the use of this keyword is crucial to the robustness and beauty of our code. The this of JavaScript is different from pure object-oriented languages such as Java and C#, which makes this even more confusing and confusing.
This is used in situations:
1. Pure function
2. Object method call
3. Use new to call constructor
4. Internal function
5. Use call / apply
6. Event binding
1. Pure function
var name = 'this is window'; //Definition The name attribute of window
function getName(){
console.log(this); //Console output: Window //this points to the global object-window object
console.log(this. name); //Console output: this is window /
}
getName();
Analysis of running results: this in pure functions all points to the global object, that is, window.
2. Object method call
var name = 'this is window'; //Define the name attribute of window to see if this.name will be called
var testObj = {
name:'this is testObj',
getName: function(){
console.log(this); //Console output: testObj //this points to the testObj object
console.log(this.name); //Console output: this is testObj
}
}
testObj.getName();
Analysis of running results: this in the called method all points to the object that called the method.
3. Use new to call the constructor
function getObj(){
console.log( this); //Console output: getObj{} //The newly created getObj object pointed to by this
}
new getObj();
Analysis of running results: this in the new constructor points to the newly generated object.
4. Internal functions
var name = "this is window"; //Definition The name attribute of window, see if this.name will be called
var testObj = {
name: "this is testObj",
getName:function(){
//var self = this; //Temporarily save this object
var handle = function(){
console.log(this); //Console output: Window //this points to the global object--window object
console. log(this.name); //Console output: this is window
//console.log(self); //The this you can get points to the testObj object
handle() ;
}
}
testObj.getName();
5. Use call / apply
var name = 'this is window'; //Define the name attribute of window to see if this.name will be called
var testObj1 = {
name : 'this is testObj1',
getName:function(){
console.log(this); //Console output: testObj2 //this points to the testObj2 object
console.log(this.name); //Console output : this is testObj2
}
}
var testObj2 = {
name: 'this is testObj2'
}
testObj1.getName.apply(testObj2) ;
testObj1.getName.call(testObj2);
Note: apply is similar to call, except that the second parameter of the two is different:
[1] call( thisArg [, arg1, arg2,... ] ); // The second parameter uses the parameter list: arg1 , arg2,...
[2] apply(thisArg [, argArray] ); //The second parameter uses the parameter array: argArray
Running result analysis: This in the function using call / apply points to the binding determined object.
6. Event Binding
This in the event method should be the most confusing place, and most errors originate from this.
//Bind on page Element
< ;script type="text/javascript">
function btClick(){
console.log(this); //Console output: Window //this points to the global object--window object
}
//Binding method in js (1)
//Binding method in js (2)
//Binding method in js (3)
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