Question

I’m inside a function of an object and I need to call an external function and pass a reference to a function as argument. This last function argument uses the keyword this several times so I need to be scoped into my object. I solved this by doing:

   MyObj.prototype.internalFunc= function(data){
       this.doSomethingWithReturnedData(data);
   };

   MyObj.prototype.doSomething= function(){
       var $this = this;
       externalFunction(this.someVar, function(data){ $this.internalFunc(data); });
   };

   var objInst = new MyObj();
   objInst.doSomething();

I want to know if there is away to avoid this messy var $this = this thing.

I also thoung of:

   //... (same as before)
   MyObj.prototype.doSomething= function(){
       var $this = this;
       externalFunction(this.someVar, this.internalFunc, this);
   };
   //... (same as before)

with

   function externalFunction(arg1, cbfunc, thisref){
       //bla bla things
       cbfunc.call(thisref, blablaData);
   };

but I also find it messy.

I think there is a better way of doing it and I’m not seeing it! Thanks in advance!

Answer 1

Assigning this to a local variable is fine and common.

Many libraries make your second approach easier by providing a method that returns a wrapper function and sets the execution context, e.g. $.proxy in jQuery (or _.bind in underscore.js).