How to distinguish mouse "click" and "drag"

Question

I think the difference is that there is a mousemove between mousedown and mouseup in a drag, but not in a click.

You can do something like this:

const element = document.createElement('div')
element.innerHTML = 'test'
document.body.appendChild(element)
let moved
let downListener = () => {
  moved = false
}
element.addEventListener('mousedown', downListener)
let moveListener = () => {
  moved = true
}
element.addEventListener('mousemove', moveListener)
let upListener = () => {
  if (moved) {
    console.log('moved')
  } else {
    console.log('not moved')
  }
}
element.addEventListener('mouseup', upListener)

// release memory
element.removeEventListener('mousedown', downListener)
element.removeEventListener('mousemove', moveListener)
element.removeEventListener('mouseup', upListener)

Cleaner ES2015

let drag = false;

document.addEventListener('mousedown', () => drag = false);
document.addEventListener('mousemove', () => drag = true);
document.addEventListener('mouseup', () => console.log(drag ? 'drag' : 'click'));

Didn't experience any bugs, as others comment.

In case you are already using jQuery:

var $body = $('body');
$body.on('mousedown', function (evt) {
  $body.on('mouseup mousemove', function handler(evt) {
    if (evt.type === 'mouseup') {
      // click
    } else {
      // drag
    }
    $body.off('mouseup mousemove', handler);
  });
});

All these solutions either break on tiny mouse movements, or are overcomplicated.

Here is a simple adaptable solution using two event listeners. Delta is the distance in pixels that you must move horizontally or vertically between the up and down events for the code to classify it as a drag rather than a click. This is because sometimes you will move the mouse or your finger a few pixels before lifting it.

const delta = 6;
let startX;
let startY;

element.addEventListener('mousedown', function (event) {
  startX = event.pageX;
  startY = event.pageY;
});

element.addEventListener('mouseup', function (event) {
  const diffX = Math.abs(event.pageX - startX);
  const diffY = Math.abs(event.pageY - startY);

  if (diffX < delta && diffY < delta) {
    // Click!
  }
});

This should work well. Similar to the accepted answer (though using jQuery), but the isDragging flag is only reset if the new mouse position differs from that on mousedown event. Unlike the accepted answer, that works on recent versions of Chrome, where mousemove is fired regardless of whether mouse was moved or not.

var isDragging = false;
var startingPos = [];
$(".selector")
    .mousedown(function (evt) {
        isDragging = false;
        startingPos = [evt.pageX, evt.pageY];
    })
    .mousemove(function (evt) {
        if (!(evt.pageX === startingPos[0] && evt.pageY === startingPos[1])) {
            isDragging = true;
        }
    })
    .mouseup(function () {
        if (isDragging) {
            console.log("Drag");
        } else {
            console.log("Click");
        }
        isDragging = false;
        startingPos = [];
    });

You may also adjust the coordinate check in mousemove if you want to add a little bit of tolerance (i.e. treat tiny movements as clicks, not drags).

If you feel like using Rxjs:

var element = document;

Rx.Observable
  .merge(
    Rx.Observable.fromEvent(element, 'mousedown').mapTo(0),
    Rx.Observable.fromEvent(element, 'mousemove').mapTo(1)
  )
  .sample(Rx.Observable.fromEvent(element, 'mouseup'))
  .subscribe(flag => {
      console.clear();
      console.log(flag ? "drag" : "click");
  });

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<script src="https://unpkg.com/@reactivex/[email protected]/dist/global/Rx.js"></script>

This is a direct clone of what @wong2 did in his answer, but converted to RxJs.

Also interesting use of sample. The sample operator will take the latest value from the source (the merge of mousedown and mousemove) and emit it when the inner observable (mouseup) emits.