JavaScript addEventListener not working with onDrop, onDragOver, or onDragStart

Question

I'm creating a simple picture puzzle game in JavaScript and am trying to implement the HTML5 Drag and Drop API. If I add an ondragstart, ondragover, or ondrop event to an element (i.e. as an attribute), it works.

However, because there are quite a few different elements in the same category I need to add event listeners to (which will only increase if I try to make a puzzle with more pieces), I'm using addEventListener to add the events. However, if I do this, it doesn't work. I've tested in Chrome and Firefox. For the record, I would really like to see if I can get this working with the HTML5 Drag and Drop API rather than with jQuery.

Here's the relevant JavaScript:

var piecesOnPage = document.querySelectorAll("#pieces img");
var puzzleSlots = document.getElementsByTagName("td");

function enableDrop(ev) {
    ev.preventDefault();
}

function dragPiece(ev) {
    ev.dataTransfer.setData("text", ev.target.id);
}

function dropPiece(ev) {
    ev.preventDefault();
    var data = ev.dataTransfer.getData("text");
    ev.target.appendChild(document.getElementById(data));
}

function createEventListeners() {
    if (piecesOnPage[0].addEventListener) {
       for (i = 0; i < piecesOnPage.length; i++) {
        piecesOnPage[i].addEventListener("dragStart", dragPiece, false);
      }
    } else if (piecesOnPage[0].attachEvent) {
        for (i = 0; i < piecesOnPage.length; i++) {
        piecesOnPage[i].attachEvent("onDragStart", dragPiece);
       }
    }

   if (puzzleSlots[0].addEventListener) {
       for (i = 0; i < puzzleSlots.length; i++) {
        puzzleSlots[i].addEventListener("drop", dropPiece, false);
   }
    } else if (puzzleSlots[0].attachEvent) {
       for (i = 0; i < puzzleSlots.length; i++) {
       puzzleSlots[i].attachEvent("onDrop", dropPiece);
      }
    }

    if (puzzleSlots[0].addEventListener) {
       for (i = 0; i < puzzleSlots.length; i++) {
        puzzleSlots[i].addEventListener("dragOver", enableDrop, false);
       }
    } else if (puzzleSlots[0].attachEvent) {
        for (i = 0; i < puzzleSlots.length; i++) {
        puzzleSlots[i].attachEvent("onDragOver", enableDrop);
       }
    }
}

if (window.addEventListener) {
   window.addEventListener("load", createEventListeners, false);
} else if (window.attachEvent) {
   window.attachEvent("onload", createEventListeners);
}

Here's the accompanying HTML. Note that, in order to demonstrate the fact that normal events work but addEventListener doesn't, I've added a normal event to the first puzzle piece and the first puzzle slot. Those work fine, but the rest don't.

<!DOCTYPE html>
<html lang="en">
<meta charset="utf-8">
<head>
<title>Puzzles</title>
<style>
    table {
    border:1px #000000 solid;
    border-collapse:collapse;
    float:right;
    margin:10px;
}

td {
    padding:0;
    line-height:0;
    height:96px;
    width:157px;
}
</style>
</head>

<body>
    <table class="puzzleboard">
        <thead></thead>
        <tbody>
            <tr><td id="space1" ondrop="dropPiece(event)" ondragover="enableDrop(event)"></td><td id="space2"></td><td id="space3"></td></tr>
            <tr><td id="space4"></td><td id="space5"></td><td id="space6"></td></tr>
            <tr><td id="space7"></td><td id="space8"></td><td id="space9"></td></tr>
        </tbody>
    </table>
    <div id="pieces">
        <img id="img1" draggable="true" ondragstart="dragPiece(event)" src="2-2.jpeg"><img id="img2" draggable="true" src="1-2.jpeg"><img id="img3" draggable="true" src="2-1.jpeg"><br>
        <img id="img4" draggable="true" src="0-2.jpeg"><img id="img5" draggable="true" src="1-0.jpeg"><img id="img6" draggable="true" src="0-1.jpeg"><br>
        <img id="img7" draggable="true" src="1-1.jpeg"><img id="img8" draggable="true" src="2-0.jpeg"><img id="img9" draggable="true" src="0-0.jpeg"><br>
    </div>
<script src="final-so.js"></script>
</body>
</html>

First Stack Overflow question ever, hope I didn't do anything TOO stupid ;)

"For the record, I would really like to see if I can get this working with the HTML5 Drag and Drop API rather than with jQuery." You do realize you don't need jquery for this.... — Phix
I know, that's actually kind of the point. It's just that whenever drag-and-drop comes up it seems that jQuery is mentioned, and I would rather just use HTML & plain JavaScript. Sorry that I didn't make that clear! '^^ — TJD

Able Johnson Able Johnson · Accepted Answer · 2017-02-21T06:36:46

Add some height and width to the img element .

<img id="img1" draggable="true" ondragstart="dragPiece(event)" src="2-2.jpeg" height="100" width="100">

this solved the issue

JavaScript addEventListener not working with onDrop, onDragOver, or onDragStart

2 Answers