The difference between apply and call
The ECMAScript specification defines two methods, call and apply, for all functions. They are widely used and their functions are exactly the same, except for passing parameters. The form is just different.
The apply method passes in two parameters: one is the object as the function context, and the other is an array composed of function parameters.
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As you can see, obj is the object used as the function context, and this in the function func points to the object obj. Parameters A and B are placed in the array and passed into the func function, corresponding to the list elements of the func parameter respectively.
The first parameter of the call method is also the object of the function context, but what is passed in later is a parameter list instead of a single array.
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Comparing apply, we can see the difference. C and D are passed to the func function as separate parameters instead of being placed in an array.
There is no need to worry about when to use which method. If your parameters already exist in an array, then naturally use apply. If the parameters are scattered and have no correlation with each other, use call.
Usage of apply and call
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We know that the first parameter of the call method is used as the function context Object, here obj is passed to func as a parameter, and this in the function points to the obj object. The func function here is actually equivalent to
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Let’s look at the example first
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From the above we can see that Person2 is instantiated The object person gets the name in Person1 through the getname method. Because in Person2, the function of Person1.call(this) is to use the Person1 object instead of this object, then Person2 has all the properties and methods in Person1, which is equivalent to Person2 inheriting the properties and methods of Person1.
The apply and call methods will cause the function to be executed immediately, so they can also be used to call functions.
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The difference between call and bind
A method called bind has been extended in EcmaScript5, but it is not compatible with lower versions of IE. It is very similar to call. It accepts two parts of parameters. The first parameter is the object as the function context, and the second part of the parameter is a list that can accept multiple parameters.
The differences between them are the following two points.
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The bind method will not be executed immediately, but will return a function that changes the context this. However, this in the original function func has not been changed and still points to the global object window.
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call passes the second and subsequent parameters as actual parameters of the func method, while the actual parameters of the func1 method are actually parameters in bind. Basically, go to the back.
在低版本浏览器没有 bind 方法,我们也可以自己实现一个。
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