Edit in JSFiddle

function tempFun() {
                this.val1 = "this.var1";
                var val2 = "var var2"; //locally scoped var, not added to function instance nor to the prototype

                this.getLocalVar = function(){
                    return val2;
                };

                this.setLocalVar = function (arg) {
                    val2 = arg;
                };                
            }
                        
            tempFun.prototype.val3 = "fun.proto.var3";
            tempFun.val4 = "fun.var4";          

            var objTempFun1 = new tempFun();
            var objTempFun2 = new tempFun();
            
            /*-----------------------------------------------------------------------
            Variables defined as `this.variableName`
            1. Are declared on prototype
            2. Have separate values across instances
            3. Cannot be accessed on function itself
            -----------------------------------------------------------------------*/
            document.write("<br />obj1-this.var1:   " + objTempFun1.val1 + "<br />");
            document.write("obj2-this.var1:   " + objTempFun2.val1 + "<br />");
            document.write("fun-this.var1:   " + tempFun.val1 + "<br />");

            objTempFun1.val1 = "this.var1x";
            objTempFun2.val1 = "this.var1y";
            document.write("obj1-this.var1:   " + objTempFun1.val1 + "<br />");
            document.write("obj2-this.var1:   " + objTempFun2.val1 + "<br />");

            /*-----------------------------------------------------------------------
            Variables defined inside function as `var variableName`
            1. Are closure-scoped; defined neither on function nor on prototype
            2. Have separate values across function instances
            3. Can only be accessed through function instance by adding methods on 
               a prototype (as above getLocalVar and setLocalVar methods)
            -----------------------------------------------------------------------*/
            document.write("obj1-var var2:   " + objTempFun1.val2 + "<br />");
            document.write("obj2-var var2:   " + objTempFun2.val2 + "<br />");
            document.write("fun-var var2:   " + tempFun.val2 + "<br />");
            document.write("obj1-printLocalVar:   " + objTempFun1.getLocalVar() + "<br />");
            document.write("obj2-printLocalVar:   " + objTempFun2.getLocalVar() + "<br />");
            objTempFun1.setLocalVar("var var2x");
            objTempFun2.setLocalVar("var var2y");
            document.write("obj1-printLocalVar:   " + objTempFun1.getLocalVar() + "<br />");
            document.write("obj2-printLocalVar:   " + objTempFun2.getLocalVar() + "<br />");
            
            /*-----------------------------------------------------------------------
            Variables defined as `functionName.prototype.variablename`
            1. Are declared on prototype
            2. Have separate values across function instances
            3. Cannot be accessed on function itself
            -----------------------------------------------------------------------*/
            document.write("obj1-this.proto.var3:   " + objTempFun1.val3 + "<br />");
            document.write("obj2-this.proto.var3:   " + objTempFun2.val3 + "<br />");
            document.write("fun-this.proto.var3:   " + tempFun.val3 + "<br />");
            objTempFun1.val3 = "fun.proto.var3x";
            objTempFun2.val3 = "fun.proto.var3y";
            document.write("obj1-this.proto.var3:   " + objTempFun1.val3 + "<br />");
            document.write("obj2-this.proto.var3:   " + objTempFun2.val3 + "<br />");

            /*------------------------------------------------------------------------
            Variables defined as `functionName.variablename`
            1. Become member of function (or say 'F'unction instance, which is tempFun) 
               not the function instances (which are objTempFun1 & objTempFun2 above)
            2. Cannot be accessed on function instances
            ------------------------------------------------------------------------*/
            document.write("obj1-fun.var4:   " + objTempFun1.val4 + "<br />");
            document.write("obj2-fun.var4:   " + objTempFun2.val4 + "<br />");
            document.write("fun-fun.var4:   " + tempFun.val4 + "<br />");