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JS Advanced - Three Calling Modes of Functions and the Pointing Problem of This

 Functions and methods are an important knowledge point in programming. The key point of a function is how to call and execute. The way it is called has a huge impact on how the code inside the function is executed, especially in the creation of the this parameter. In addition to the most basic calling method such as function name (), what other methods are there? The following briefly introduces the three most basic (excluding, bind, apply, call).

  • The function is actually inanimate, we need to give it life (call) before it can withdraw its value
  • Functions are created with two default parameters, this and arguments

Function creation is divided into two types: declarative and expression, which can be called directly through the function name ()

        function fun(){
            console.log(this)
            console.log(arguments);
        }
        fun(1,100);

Called by means of an object, this points to the object

 function fun(){
            console.log(this)
            console.log(arguments);
        }
        // fun(1,100);
        let obj={id:1001,fn:fun};
        obj.fn();

Called by the constructor, this points to the instance object of the constructor

 function fun(){
            console.log(this)
            console.log(arguments);
        }
        // fun(1,100);
        // let obj={id:1001,fn:fun};
        // obj.fn();
        new fun();
        console.log(new fun() instanceof fun);


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