Is object creation delayed when managed into a P5js instance?

nemecsek69 · May 2018

As my knowledge of JS is extremely limited, I cannot properly describe the issue: it is more a curiosity than a real problem (it took me some time to pinpoint it).

Here I am creating 2 objects, setting the type variable ONLY AFTER calling the object creation. It looks like the object is not created immediately but only in a second time, after the variable has been set, even if the lines order would hint otherwise.

Is this JS or P5.js related? Is this due to hoisting?

I would like, for my own knowledge, to be directed to the proper docs in order to understand what is happening here. Thanks

<html>
<head>
    <script type="text/javascript" src="static/js/p5.min.js"></script>
</head>
<body>
    <script>
        let sketch = function (p) {
            p.setup = function () {
                alert("Creating " + p.type);
            };
        };

        let objA = new p5(sketch);
        objA.type = "A";      // <--- AFTER creating the object?!?

        let objB = new p5(sketch);
        objB.type = "B";
    </script>
</body>
</html>

GoToLoop · May 2018

let sketch = function (p) {
    p.setup = function () {
        alert("Creating " + p.type);
    };
};

let objA = new p5(sketch);
console.log(objA.type); // undefined
objA.type = "A";

let objB = new p5(sketch);
console.log(objB.type); // undefined
objB.type = "B";

GoToLoop · May 2018

The sketch variable is passed to p5's constructor as a callback.
In order to know when that callback is actually invoked, we'd need to study p5.js' source code.
Also notice that setup() is a callback of the sketch callback.
Until the execution reaches the alert() inside setup(), the property type had been assigned to "A" a long time ago.

nemecsek69 · May 2018

Thank you, @GoToLoop! I thought I was missing something very important about Javascript.

GoToLoop · May 2018

Is this due to hoisting?

Hoisting only works for variables declared w/ keywords var & function. :-B
Given type isn't even a variable but an object property, hoisting isn't applied to it in any case. :\">

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Is object creation delayed when managed into a P5js instance?

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