Drag'n'drop dataTransfer.getData empty

Question

I'm trying to get drag'n'drop to work, but I seem to be completely missing how the getData/setData works.

I'm using this code (http://jsfiddle.net/ASKte/218/)

var el = angular.element(document.getElementById('drag'));
el.attr("draggable", "true");
el.bind("dragstart", function(e) {
    e.dataTransfer.setData('text', 'Where have you gone?!?!')         
});

var target = angular.element(document.getElementById('drop'));
target.bind("dragover", function(e) {
    if (e.preventDefault) {
        e.preventDefault(); // Necessary. Allows us to drop.
    }
    return false;
});

target.bind("dragenter", function(e) {
    console.debug(e.dataTransfer.types);
    console.debug(e.dataTransfer.getData('text'));
});

I'm using AngularJS here because this is a snippet of a much larger piece of code.

For some reason when dragging the top square on the bottom square, the value of getData('text') is always empty, but I have no idea why...

Any ideas?

Thanks in advance.

Answer 1

The data is only available on drop, this is a security feature since a website could grab data when you happen to be dragging something across the webpage.

var el = angular.element(document.getElementById('drag'));
el.attr("draggable", "true");
el.bind("dragstart", function(e) {
    e.dataTransfer.setData('text', 'Where have you gone?!?!')         
});

var target = angular.element(document.getElementById('drop'));
target.bind("dragover", function(e) {
    if (e.preventDefault) {
        e.preventDefault(); // Necessary. Allows us to drop.
    }
    return false;
});

target.bind("drop", function(e) {
    console.debug(e.dataTransfer.types);
    console.debug(e.dataTransfer.getData('text'));
});  

<script src="https://ajax.googleapis.com/ajax/libs/angularjs/1.2.23/angular.min.js"></script>
<div id="drag" style="width: 100px; height: 100px; background-color: blue;"></div>

<div id="drop" style="width: 100px; height: 100px; background-color: green;"></div>

Answer 2

If you really need to access data in other drop-events, use dataTransfer.types. Use JSON.parse, JSON.stringify and encode/decode uppercase characters to get around dataTransfer.types getting lower cased.

Setting data:

event.dataTransfer.setData(encodeUpperCase(JSON.stringify(value)), '');

Getting data:

const data = JSON.parse(decodeUpperCase(event.dataTransfer.types[0]))

Where the encoding/decoding goes something like this:

  const UPPERCASE_PREFIX = '^{';
  const UPPERCASE_SUFFIX = '}^';

  function encodeUpperCase(str: string): string {
    return str.replace(/([A-Z]+)/g, `${UPPERCASE_PREFIX}$1${UPPERCASE_SUFFIX}`);
  }

  function decodeUpperCase(str: string): string {
    const escapeRegExp = (escape: string) => ['', ...escape.split('')].join('\\');

    return str.replace(
      new RegExp(`${escapeRegExp(UPPERCASE_PREFIX)}(.*?)${escapeRegExp(UPPERCASE_SUFFIX)}`, 'g'),
      (_, p1: string) => p1.toUpperCase()
    );
  }

It works, but you might summon Cthulhu in the process.