Examples to explain how to solve this pointing error in JavaScript (picture and text tutorial)-JS Tutorial-php.cn

Examples to explain how to solve this pointing error in JavaScript (picture and text tutorial)

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Release： 2018-05-21 09:48:23

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The handling of this pointer in JavaScript is a common headache for everyone. Here we give an example to explain the solution to the this pointer error in JavaScript. Friends in need can refer to

to see the following object definition:

&#39;use strict&#39;
var jane = {
  name ： ‘Jane&#39;,
  display : function(){
    retrun &#39;Person named &#39; + this.name;
  }
};

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This way you can call it normally

jane.display();

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The following call will go wrong:

var func = jane.display;
func()

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TypeError: Cannot read property &#39;name&#39; of undefined

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Because this pointer has changed, the correct way is as follows:

var func2 = jane.display.bind(jane);
func2()

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&#39;Penson named Jane&#39;

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All functions have their special this variable, such as the following forEach

var jane = {
  name : &#39;Jane&#39;,
  friends: [&#39;Tarzan&#39;, &#39;Cheeta&#39;],
  sayHiToFriends: function(){
    &#39;use strict&#39;;
    this.friends.forEach(function(friend) {
      // &#39;this&#39; is undefined here
      console.log(this.name + &#39; says hi to &#39;+ friend);
    });
  }
}

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Calling sayHiToFriends produces an error:

jane.sayHiToFriends()

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TypeError: Cannot read property &#39;name&#39; of undefined

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Solution One: Save this in different variables

var jane = {
  name : &#39;Jane&#39;,
  friends: [&#39;Tarzan&#39;, &#39;Cheeta&#39;],
  sayHiToFriends: function(){
    &#39;use strict&#39;;
    var that = this;
    this.friends.forEach(function(friend) {
      console.log(that.name + &#39; says hi to &#39;+ friend);
    });
  }
}

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Solution two:Use the second parameter of forEach, It can assign a value to this

var jane = {
  name : &#39;Jane&#39;,
  friends: [&#39;Tarzan&#39;, &#39;Cheeta&#39;],
  sayHiToFriends: function(){
    &#39;use strict&#39;;
    this.friends.forEach(function(friend) {
      console.log(this.name + &#39; says hi to &#39;+ friend);
    }, this);
  }
}

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The above is what I compiled for everyone. I hope it will be helpful to everyone in the future.

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