JavaScript, a function in JS, the first sentence var _this = This; Why do you do this?

JavaScript, a function in JS, the first sentence var _this = This; Why do you do this? Here is the source code:

1 The following code is a common site home page, automatically switch span or Tabbar to change the list display content of the key method:2 functionScrolldoor () {3 }4Scrolldoor.prototype = {5Sd:function(menus,divs,openclass,closeclass) {6 var_this = This;//you see clearly, here, why not directly with this, to use _this instead of all the following this, what is the special significance? What happens if I use this? A total of 2 questions ha!7 if(Menus.length! =divs.length)8 {9Alert ("The number of menu layers and content layers is different!"));Ten return false; One }  A  for(vari = 0; i < menus.length; i++) - {  -_this.$ (Menus[i]). Value =i; the_this.$ (Menus[i]). onmouseover =function(){ -  -  for(varj = 0; J < Menus.length; J + +) - {  +_this.$ (Menus[j]). ClassName =Closeclass; -_this.$ (Divs[j]). style.display = "None"; + } A_this.$ (menus[ This. value]). ClassName =Openclass; at_this.$ (divs[ This. value]). style.display = "Block";  - } - } - }, -$ :function(OID) { - if(typeof(OID) = = "string") in returndocument.getElementById (OID); - returnOID; to } +}

question one: I do not know whether the landlord has contacted jquery jquery inside there is a particularly typical example can be illustrated with the role of _this $ ("#btn"). Click (function () {var_this = This;//this and _this both represent the object of "#btn."$(". TR"). each (function () { This;//here This represents each of the ". Tr" objects that are traversed_this;//still stands for "#btn" Object}) This is the case in a code fragment where this may represent different objects, and the coder wants _this to represent the original object Problem 2: In fact, not all use _this but as far as I can see, there should be no difference, the landlord of the Code with _ This is probably just for coding specifications.

You give the example gave me a good inspiration, because JS can be nested code layers, may also be nested below a method, reference this will become sub-method control of the object, if the need for superior to the image, in the case of no parameters, the front premise made a temporary variable _this, can save the superior to the image, Sub-methods can be called with _this, this is the purpose.     Perhaps as you said, in my method, there is no nested method in the back, it is probably just for coding specifications.

JavaScript, a function in JS, the first sentence var _this = This; Why do you do this?