from You dont know js on github
To learn this, you first have to learn what this is not, despite any assumptions or misconceptions that may lead you down those paths. this is neither a reference to the function itself, nor is it a reference to the function’s lexical scope.
this is actually a binding that is made when a function is invoked, and what it references is determined entirely by the call-site where the function is called.
me: this 在单纯的函数声明方式中表示 Grobal Object，在作为对象的函数时指代对象。