Class-wide Event is Malfunctioning

Question

I create a 16x16 grid of divs in JavaScript. Each div has a mouse enter event (inherited based on common class) that should change its black background to white.

Here's my problem: whereas each div should change color when it's hovered over, all divs (when hovered over) cause the same bottom-right div to change color, rather than themselves.

I believe all of the events reference the final div under the className "squares" (bottom right div). How do I make each event reference its own div?

SNAPSHOT

CODE

    //GRID CREATION (30x30)
    var container = document.getElementById('container');
    var size = 30;

    //Row Creation (30)
    for(j=0; j < size; j++) {
        var row = document.createElement('div');
        row.classList.add("row");

        //Square Creation (30 per Row)
        for(i=0; i<size; i++) {
            var square = document.createElement('div')
            square.classList.add("square");

            //div background-color changes on mouse-enter   
            square.addEventListener('mouseenter', () => { 
                this.square.style.background = 'white';
            });

            row.appendChild(square);
        }
        container.append(row);
    }

You need to create a closure, because `this` is applying to the final iteration of the loop. Create a function, pass in `this` and change the background there — Sterling Archer, Apr 06 '18 at 00:51
@SterlingArcher: `this` is the same across all of the loop iterations though — Ry-, Apr 06 '18 at 00:51
@Ry︁ right, but assuming `this` is a class reference, even removing `this`, wouldn't it be bound outside of the loop? — Sterling Archer, Apr 06 '18 at 00:53
@Ry @SterlingArcher I originally did not have `this` and the same problem existed: all events affected the bottom-right div only — Ben, Apr 06 '18 at 00:55

score 1 · Accepted Answer · answered Apr 06 '18 at 00:56

It’s strange to find this.square in your event listener when nothing else refers to this.square. Perhaps you originally tried square.style.background, which didn’t work for the reason described in JavaScript closure inside loops – simple practical example, then tried to fix it with this.style.background = 'white';, which didn’t work because it was an arrow function, then tried to make this.square work…?

Anyway, use either a non-arrow function, to get this inside to be the element the event listener was attached to instead of the same as the this outside:

square.addEventListener('mouseenter', function () { 
    this.style.background = 'white';
});

or better, declare your variables with let – which must be available, since you were using an arrow function – and refer to square:

//GRID CREATION (30x30)
let container = document.getElementById('container');
let size = 30;

//Row Creation (30)
for (let j = 0; j < size; j++) {
    let row = document.createElement('div');
    row.classList.add("row");

    //Square Creation (30 per Row)
    for (let i = 0; i < size; i++) {
        let square = document.createElement('div');
        square.classList.add("square");

        //div background-color changes on mouse-enter   
        square.addEventListener('mouseenter', () => { 
            square.style.background = 'white';
        });

        row.appendChild(square);
    }
    container.append(row);
}

Declarations for j and i were missing, too. You should enable strict mode and never use var to avoid these types of problems.

Class-wide Event is Malfunctioning

1 Answers1