Pattern of the reference to this object in instance method.

ref.js

function Obj(){
    this.prop = 'PROP';
}

Obj.prototype.refToProp = function(){
    // Only self can refer to the Obj instance object.
    // So if you want to refer in other function, self variable is need to be defined.
    var self = this;
    setTimeout(function(){
        console.log(self.prop);
    },1000);
}