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This is a feature in Javascript that is very easy to misunderstand and then use incorrectly. Therefore, the following article mainly introduces to you the relevant information about the problem of this keyword pointing in Javascript. The test questions in the article test your familiarity with this. Friends in need can refer to it. Let's take a look together.
Preface
Javascript is an object-based dynamic language, that is to say, everything is an object. A typical example is that functions are also treated as ordinary objects. Javascript can implement object-oriented programming through certain design patterns, in which this "pointer" is a very important feature in realizing object-oriented programming. This article will give you a detailed introduction to the relevant content pointed to by the this keyword in Javascript. Let us do a small test first. If you get all the answers correct, congratulations, you don’t need to read any further.
Test questions
First question
Second question
Third question
Question 4
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Answer
this
#1. Point to the object of the calling function
First of all, let’s understand what apply()/call() is?
function.call([thisObj[,arg1[, arg2[, [,.argN]]]]]) function.apply([thisObj[,argArray]])
1. Call the function function, but this in the function points to thisObj (change the internal pointer of the object)
2. If thisObj is not passed parameter, the default is the global object
3. Contact and difference between call()/apply()
Contact: The function is the same, the first parameter is thisObj
Difference: If there are more parameters passed
The actual parameters of call() are listed one by one
The actual parameters of apply() The parameters are all placed in the second array parameter
An example of understanding apply()/call():
The fourth usage example of this
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