The problem with the function scope object

[espruino-discuss]

Posted at 2017-12-05 by Konkery

There is an object created via new:

function class_1()
{
this.A_1;
this.B_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.A_2;
this.B_2;
this.Obj_2 = _obj;
}

class_2.prototype.func_class_2  = function()
{
	//function call problem !!!
	this.Obj_2.func_class_1();
}

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()" ?

[espruino-discuss]

Posted at 2017-12-05 by @gfwilliams

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.

---

Posted at 2017-12-05 by Konkery

Thank you for such a quick response !
I use the cost of production of Amperka (http://amperka.ru/) - "IskraJS" based on Espruino 1v92.194

---

Posted at 2017-12-05 by Konkery

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.PHASE_ARR = [ "START_MOVE", "START_WAIT", "DOWN_MOVE", "DOWN_WAIT", "UP_MOVE", "UP_WAIT" ];
	
	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]; 
		}
		
	switch(_this.CurPhase)
	{
		case "START_MOVE":
							if( !_this.FlagSTART_MOVE )
							{
								_this.Obj1.AnimationTask(_this.ANGLE_START, _this.SPEED_START);
									_this.FlagSTART_MOVE = true;
							}
							else
							{
								if ( !_this.Obj1.GetStatusRunAnimation() ) //Error !
								{
									_this.CurPhase = _this.PHASE_ARR[1]; 
										_this.FlagSTART_MOVE = false; 
								}
							}
							
			break;
};

---

Posted at 2017-12-05 by @gfwilliams

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.

---

Posted at 2017-12-05 by Konkery

Thanks again !
Already sent a request to Amperka

---

Posted at 2017-12-10 by Konkery

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

---

Posted at 2017-12-11 by @gfwilliams

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

---

Posted at 2017-12-11 by Konkery

Yes, "this" was lost in one of setTimeout

---

Posted at 2017-12-11 by @allObjects

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

• You can pass parameter for the function in

setTimeout(function(_, otherParms,...){
    _.memberOfContextObject;
    _.memberOfContextObject();
  }, timeoutTimeInMS, contextObject, otherParms,...);

• Alternative is to bind the function and then pass to `

setTimeout(function(otherParms,...){
    this.memberOfContextObject;
    this.memberOfContextObject();
  }.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
  setTimeout(function(otherParms,...){
      _this.memberOfContextObject;
      _this.memberOfContextObject();
    }, 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.

---

Posted at 2017-12-11 by PaddeK

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

---

Posted at 2017-12-12 by Konkery

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 */
	this.Obj.func_1();
}

---

Posted at 2017-12-13 by @allObjects

...?

...do not exactly get what above code should proof or disproof...

(function(){
var MyClassA = function(name, checkInInterval)
  {
    this.name = 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();
    console.log(Math.floor(time)
       + ": Hi, my name is " + this.name
       + "; " + this.commander.name
       + " commanded me to check in"
       + " every " + (this.checkInInterval / 1000)
       + " seconds. --- Bye!");
  }

var MyClassB = function(name, _object)
  {
    this.name = name;
    this.Obj = _object;
  }
MyClassB.prototype.func_1 = function()
  {
    /* here some code */
    this.Obj.func_1(this);
  }

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);
    objBen.func_1();
    objBob.func_1();
  }
  
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!

...you 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.