This mechanism in JavaScript and javascriptthis Mechanism

This mechanism in JavaScript and javascriptthis Mechanism

JavaScript has its own set of this mechanism. In different cases, the point of this varies.

Global range

Console. log (this); // global variable

In the global range, this is used to point to the global variable. In the browser environment, this is the window.

Note: The strict mode of ECMAScript5 does not have a global variable. here this is undefined.

Function calling

Function foo () {console. log (this);} foo (); // global variable

This in function call also points to global variables.

Note: The strict mode of ECMAScript5 does not have a global variable. here this is undefined.

Object method call

Var test = {foo: function () {console. log (this) ;}} test. foo (); // test object

In an object method call, this points to the caller.

Var test = {foo: function () {console. log (this) ;}} var test2 = test. foo; test2 (); // global variable

However, due to the late binding feature of this, in the above case, this will point to a global variable, which is equivalent to directly calling a function.

This is very important. For the same code segment, this point can be determined only at runtime.

Constructor

Function Foo () {console. log (this);} new Foo (); // the newly created object console. log (foo );

Inside the constructor, this points to the newly created object.

Explicitly set this

Function foo (a, B) {console. log (this) ;}var bar ={}; foo. apply (bar, [1, 2]); // barfoo. call (1, 2); // Number object

Using the call or apply method of Function. prototype, this is set to the first parameter passed in.

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