This understanding in js and jsthis understanding

This understanding in js and jsthis understanding

In js, this is used in four categories:

(1) pure function call: The most common usage is global call, which is equivalent to window

(2) call as an object method: this refers to this parent object.

(3) As a constructor call: new generates a new object. this indicates the new object.

(4) apply call: apply is a method of a function object. Its function is to change the function call object. Its first parameter indicates the object that calls the function after the change, this indicates the first parameter of the function.

When the apply parameter is null, global objects are called by default.

For details, refer:

Http://www.ruanyifeng.com/blog/2010/04/using_this_keyword_in_javascript.html)

Http://javascript.ruanyifeng.com/oop/basic.html)