为什么将'this'对象分配给js中的局部变量

Question

I was going through ext-all-debug.js file from extjs library and most of the class methods had

var me = this;

How does it helps in performance?

Answer 1

It doesn't help in performace but when the function is called in a different scope you still have the pointer to the expected object

function someFunc() {
    var me = this;
    someElement.on("click", function() {
        console.log(me);
        console.log(this);
    });
};

when this is logged the console will show the caller of the function. In the case where me is logged it will show the element that was clicked on

Answer 2

It doesn't help with performance. It helps with confusion. this gets reassigned a lot, automatically. If you want to remember what this is, you assign it to something else, traditionally me , self or that . Or you use bind . It also helps with compression, since me can be compressed to a one-letter variable, but only this is magical and can't be renamed.

Answer 3

It is not performance related. However by this way it declares a var that can be accessed by other members within this “Closure”. Noted that the "this" of the other members is not determined by the definition context, "this" is whoever calls the function. On the contrary, variant scope is always determined by the definition context.