The problem with the function scope object

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  • There is an object created via new:

    function class_1()
    class_1.prototype.func_class_1 = function()
            here are some actions with variables this.A_1, this.B_1
    function class_2 (_obj /*object of type class_1*/)
    this.Obj_2 = _obj;
    class_2.prototype.func_class_2  = function()
        //function call problem !!!
    var o1 = new class_1();
    var o2 = new class_2(o1);
    o2.func_class_2(); //Uncaught Error: Field or method "func_class_1()" does not already exist, and can't create it on undefined

    Help !
    I tried various options with this, call and bind, nothing helped. How to organize a call to "this.Obj_2.func_Class_1()" ?

  • Which firmware version are you running this on, and on what device?

    I just ran this on the latest builds and it works fine.

    However: If you put this in the right-hand side of the web IDE you get loads of errors. I'd fix those first.

    Specifically what do you intend to do with this.A_1;/etc? You're just referencing fields that don't exist yet, without setting them to anything.

  • Thank you for such a quick response !
    I use the cost of production of Amperka ( - "IskraJS" based on Espruino 1v92.194

  • In the code there are no syntax errors it builds and runs fine, below part of code:

    function TObj_1(_pin)
        /*** константы класса ***/
        this.MinPulse = 453.0; //минимальная длительность импульса которая соответствует крайнему "меньшему" положения ротора
        this.MaxPulse = 2050.0; //макисмальная длительность импульса которая соответствует крайнему "меньшему" положения ротора
        this.Ks = 8.7; //коэффициент преобразования в ф-ции Y=kA+B (линейная кривая самого сервопривода
        /*** поля класса ***/
        this.Pin = null; //пин микропроцессора на котором "сидит" сервопривод
        this.Value = 0.0; //конечное значение яркости свечения
        this.CurValue = 0.0; //текущее значение яркости свечения
        this.Speed = 0.0; //текущая скорость процесса
        this.Pin = _pin; //задать пин к которому привязан сервопривод
    TObj_1.prototype.BunRunAnimation = function()
        this.FlagBunAnimation = true; //запретить "ручной" запуск Animation(...)
            this.StopAnimation(); //остановить текущую анимацию
    function TObj_2(_tobj_1)
        this.ANGLE_START = 30; //конечный угол ротора фазы START_MOVE
        this.ANGLE_UP = 20; //конечный угол ротора фазы UP_MOVE
        this.ANGLE_DOWN = 0; //конечный угол ротора фазы DOWN_MOVE
        this.TIME_START = 15; //время нахождения в позиции START_WAIT, секунд
        this.TIME_UP = 0.5;  //время нахождения в позиции UP_MOVE, секунд
        this.TIME_DOWN = 0.7;  //время нахождения в позиции UP_WAIT, секунд
        this.SPEED_START = 25; //скорось движения ротора в фазе START_MOVE, %/s
        this.SPEED_UP = 40;  //скорось движения ротора в фазе UP_MOVE, %/s
        this.SPEED_DOWN = 25;  //скорось движения ротора в фазе DOWN_MOVE, %/s
        this.INTERVAL_PLAY = 60.0; //определяет период в ms запуска внутренней ф-и setTimeout
        this.Obj1 = _tobj_1; //инициируем поле объектом класса Servo
    TObj_2.prototype.TaskRun = function()
        let _this = this;
        if( !_this.FlagTaskRun )
                _this.FlagTaskRun = true; 
                    _this.Obj1.BunRunAnimation(); //Error !
                _this.CurPhase = _this.PHASE_ARR[0]; 
            case "START_MOVE":
                                if( !_this.FlagSTART_MOVE )
                                    _this.Obj1.AnimationTask(_this.ANGLE_STA­RT, _this.SPEED_START);
                                        _this.FlagSTART_MOVE = true;
                                    if ( !_this.Obj1.GetStatusRunAnimation() ) //Error !
                                        _this.CurPhase = _this.PHASE_ARR[1]; 
                                            _this.FlagSTART_MOVE = false; 
  • Moving this to 'other boards' - IskraJS isn't an official board - they're just using the Open Source Espruino firmware.

    I've tried to run your code even on a 1v92 version of Espruino and it works (without the Exception) - perhaps you could contact Amperka to see if they can help you out.

  • Thanks again !
    Already sent a request to Amperka

  • The problem is solved. Loss of context occurred in one of the plugins. The firmware of the Amperka code executes correctly.

  • Great! By 'loss of context', you mean you called it in a setTimeout or something?

  • Yes, "this" was lost in one of setTimeout

  • JavaScript provides you with standard means to ensure the desired context:

    • You can pass parameter for the function in

    setTimeout(function(_, otherParms,...){
      }, timeoutTimeInMS, contextObject, otherParms,...);
    • Alternative is to bind the function and then pass to `

      }.bind(contextObject), timeoutTimeInMS, otherParms,...);
    • This works too, but is not as flexible as above options:

    function anyFunctionOfThis() {
      var _this = this; // create non-this reference of this
        }, timeoutTimeInMS, otherParms,...);

    As you know, you can defined the function as a named function outside of setTimeout(... or setInterval(... or ..., functionAsCallbackParm,...either as function or 'method of an object' (see object-oriented programming with JS). I use this when I have to provide them as callbacks in multiple places:

    var fun      = function(otherParms,...) { ... };
    var funBound = fun.bind(contextObject);
    setTimeout(funBound, timoutTimeInMS, otherParms,...

    There are many options and combinations there of you can chose from for the optimal use in your situation.

    For the alternative 'this', I use the _this or short form of it _ to indicate that it is about the this / context object. I've also seen that to be used. But I prefer a more eye catching - and short - form, therefore: _ is my choice.

  • Or.. if the contextObject you need is the outer scope just use a arrow function as setTimeout callback and be done with it.

    Other public choices for the this alter ego are me and self :D

  • Thank you all for the advice !

    function myclassA()
        this.A = 1;
        this.TimerID = null;
    myclassA.prototype.func_1 = function()
        /* here some code */
        this.TimerID = setInterval(this.func_2.bind(this), 50);
    myclassA.prototype.func_2 = function()
        /* There was an error ! )) */
    function myclassB(_object)
        this.B = 1;
        this.Obj = _object;
    myclassB.prototype.func_1 = function()
        /* here some code */
  • ...? not exactly get what above code should proof or disproof...

    var MyClassA = function(name, checkInInterval)
      { = name;
        this.checkInInterval = checkInInterval;
        this.TimerID = null;
        this.commander = null;
    MyClassA.prototype.func_1 = function(commander)
        /* here some code */
        this.commander = commander;
        this.TimerID = setInterval(this.func_2.bind(this), this.checkInInterval);
    MyClassA.prototype.func_2 = function()
        var time = (typeof getTime != "undefined") ? getTime() : new Date().getTime();
           + ": Hi, my name is " +
           + "; " +
           + " commanded me to check in"
           + " every " + (this.checkInInterval / 1000)
           + " seconds. --- Bye!");
    var MyClassB = function(name, _object)
      { = name;
        this.Obj = _object;
    MyClassB.prototype.func_1 = function()
        /* here some code */
    var objAlf, objAnn, objBen, objBob;
    var onInit = function()
        objAlf = new MyClassA("Alf",2000);
        objAnn = new MyClassA("Ann",5000);
        objBen = new MyClassB("Ben",objAlf);
        objBob = new MyClassB("Bob",objAnn);
    setTimeout(onInit, 1000);

    Should run in Espruino and provide output in the console like that:

    1513144683321: Hi, my name is Alf; Ben commanded me to check in every 2 seconds. --- Bye!
    1513144685319: Hi, my name is Alf; Ben commanded me to check in every 2 seconds. --- Bye!
    1513144686318: Hi, my name is Ann; Bob commanded me to check in every 5 seconds. --- Bye!
    1513144687321: Hi, my name is Alf; Ben commanded me to check in every 2 seconds. --- Bye!
    1513144689322: Hi, my name is Alf; Ben commanded me to check in every 2 seconds. --- Bye!
    1513144691320: Hi, my name is Alf; Ben commanded me to check in every 2 seconds. --- Bye!
    1513144691321: Hi, my name is Ann; Bob commanded me to check in every 5 seconds. --- Bye!
    1513144693321: Hi, my name is Alf; Ben commanded me to check in every 2 seconds. --- Bye!
    1513144695319: Hi, my name is Alf; Ben commanded me to check in every 2 seconds. --- Bye!
    1513144696318: Hi, my name is Ann; Bob commanded me to check in every 5 seconds. --- Bye!
 can also just open the debugger of (chrome) browser (with 'right-click' Inspect) and paste the code into the console... :)

    As the output shows, Alf - objAlf - and Ann - objAnn- know still about their names, their time interval to show up, and who commanded them: Ben and Bob.

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The problem with the function scope object

Posted by Avatar for Konkery @Konkery