getter in p5.js

strinda

Hi! Have the following questions. I need do define a function that will change one parameter of an abject:

this.setCoordinates (coordX,  coordY) = function ()  {
this.location.x = coordX - this.location.x;
this.location.y = coordY - this.location.y;
}

Above is the piece of code. CoordX and coordY will be sent to the object this way. What is the correct syntaxis?

strinda

Not sure this is needed. This is the whole obeject:

function waterRock () {
this.location = createVector (100, 100);  
this.radius = random (25,75);
this.id = random (1,100);

this.display = function() {
fill (255);
ellipse (this.location.x, this.location.y, this.radius,this.radius);
text (this.id, this.location.x, this.location.y);
}

this.setCoordinates (coordX,  coordY) = function ()  {
this.location.x = coordX - this.location.x;
this.location.y = coordY - this.location.y;

text (this.location.x, 600,200);
text (this.location.y, 600,250);
}

}

And this is how I change the parameteres:

for (i=0; i <1; i++) { 
   waterRocks[i].setCoordinates(300, 300);
   waterRocks[i].display();
   print (i);
}

GoToLoop

• Class names should be UpperCamelCase: Rename waterRock to WaterRock! L-)
• @ #12 this.setCoordinates(coordX, coordY) = function () {};, you're not defining a function!
• Instead, you're attempting to invoke some non-existing function called setCoordinates(), passing variables coordX & coordY as its arguments.
• And even worse, you're trying to assign another function to its returned value!!! @-)
• In order to define a function, we can use JS' keyword function:
  https://developer.Mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/function
• In your case that'd be: function (coordX, coordY) {}
• Now you can assign it to WaterRock's property setCoordinates: O:-) this.setCoordinates = function (coordX, coordY) {};

GoToLoop

• However, defining methods inside their class' constructor aren't memory savvy!
• B/c every time you instantiate the class, you also unnecessarily duplicate all of its methods, thus wasting RAM! :-SS
• Rather, define them all outside the constructor's function, annexing each method to its class' prototype, like this: WaterRock.prototype.setCoordinates = function (coordX, coordY) {};
• Or better yet, abandon this ancient way of doing OOP, and embrace ES6 class keyword: \m/

https://developer.Mozilla.org/en-US/docs/Web/JavaScript/Reference/Classes

strinda

Still don't fully get it. 1) Isn't this EXACTLY waht they do here? https://p5js.org/examples/objects-objects-2.html

initializing a function - as a method? this.move = function(posX, posY, damping)

2) Also, as for this ECMAScript 6, do you think it can be used in Openprocessing.org?

3) Rather, define them all outside the constructor function, annexing each method to its class' prototype, like this - is there a reference for that anywhere?

Thank you in advance.

GoToLoop

1) Compare their this.move = function (posX, posY, damping) {};
to your this.setCoordinates(coordX, coordY) = function () {};.
They're clearly different! Your version is attempting to call setCoordinates() instead of defining it! b-(

Remember, we define functions/methods via keyword function. :-B
Then later we suffix the operator () after its name in order to invoke it. *-:)

strinda

Ok, what if i change it to: this.setCoordinates= function (coordX, coordY) {};

It will work for sure, but you still say it is not a good way, right?

GoToLoop

2) Our JS code depends on the VM version running it, not the server hosting it. ;;)

3) That's called Prototype Pattern: https://developer.Mozilla.org/en-US/docs/Web/JavaScript/Introduction_to_Object-Oriented_JavaScript#Prototype-based_programming

Take a look below on how methods should be defined using this ancient pattern:
https://developer.Mozilla.org/en-US/docs/Web/JavaScript/Introduction_to_Object-Oriented_JavaScript#The_methods

Repeating again, forget about it. Just embrace the modern ES6 keyword class:
https://developer.Mozilla.org/en-US/docs/Web/JavaScript/Reference/Classes

That's much easier. Especially for us coming from Java! ~O)

strinda

Ok, I will. Thank you!