JavaScript class property cannot be found

Question

I have this snippet of code. I am very new to JavaScript, and I have an error in:

class X {
    constructor() {
      this.pick = -1;
      this.isClosed = false;
      this.pline = [];
    }

  add(mx, my) {
    pline.push(Point(mx,my));
  }
  
  draw() { 
    beginShape();
    for (let i = 0; i < pline.length; i++) {
        p = pline[i];
        vertex( p.x, p.y );
    }
    ... //ignore the rest for now

the issue I am getting is: X, line 14:ReferenceError: Can't find variable: pline

I am a little confused because I am initializing it as a class property, so I am not sure why it cannot be found in the draw function. Any help is highly appreciated.

its hidden as an class property... try to change from `pline` to `this.pline` — Mykola Kikets, Sep 04 '22 at 18:06

score 2 · Answer 1 · answered Sep 04 '22 at 18:06

This is because you have scoped pline to this, so it must be this.pline.push.

Also, if you want to use this scope, it's best to use arrow function methods to maintain the scope. Example:

class clazz{
    constructor() {
        this.something = 1;
    }
    
    add = () => {
        
        console.log(this.something);
        
    };
}

score 2 · Answer 2 · answered Sep 04 '22 at 18:06

pline refers to a variable (either local or global), not a property. If you want to access a property, then you must use this.pline. Although variables and properties seem the same, under the hood they are fairly different because of how JavaScript classes work (which is quite different from most languages).

score 1 · Answer 3 · answered Sep 04 '22 at 18:08

1

in your add() function you are referring to "pline.push()", you need to use this.pline.push()

answered Sep 04 '22 at 18:08

Oscar Nilsson

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JavaScript class property cannot be found

3 Answers3