Private variable in java script.

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Javascript

I want to declare private object in java script. I have decided all private variable is of type local. So I have created following method.
I have following 2 option of doing declaration.

var helper=helper||{};

function(publicMethod){
var privateMthod={}; //Option1
var privateMethod=this; //Option2

privateMethod.complexTask=function(){
//some code...
}

publicMethod.f1=function(){
   privateMethod.complexTask();
}
}(helper)

Which option is correct Option1 and Option2?
What is deference between Option1 and Option2?