There’s no way to catch an event on the blue one, because the red is on top: And mouse events only happen on the top element, not on those below it.įor instance, below are two elements, red one on top of the blue one (fully covers). The problem is that, while we’re dragging, the draggable element is always above other elements. What may be the first idea? Probably to set mouseover/mouseup handlers on potential droppables? The solution is kind-of interesting and just a little bit tricky, so let’s cover it here. and, preferably, know the droppable we’re dragging over, to highlight it.where the element was dropped at the end of Drag’n’Drop – to do the corresponding action,.Speaking abstract, we take a “draggable” element and drop it onto “droppable” element. For instance, a “file” into a “folder” or something else. In real-life we usually take one element and drop it onto another. In previous examples the ball could be dropped just “anywhere” to stay. Now it fluently follows the pointer from the current position. In the previous example the ball “jumps” under the pointer. The difference is especially noticeable if we drag the ball by its right-bottom corner. On the beginning of the drag’n’drop, the ball “forks”: we start dragging its “clone”. If we run the code, we can notice something strange. (3) drop the ball, remove unneeded handlersĭocument.removeEventListener('mousemove', onMouseMove) move our absolutely positioned ball under the pointerĭocument.addEventListener('mousemove', onMouseMove) centers the ball at (pageX, pageY) coordinatesī = pageX - ball.offsetWidth / 2 + 'px' ī = pageY - ball.offsetHeight / 2 + 'px' to make it positioned relative to the body move it out of any current parents directly into body (1) prepare to moving: make absolute and on top by z-index Here’s the implementation of dragging a ball:
Java mouse coordinates offset how to#
Later we’ll see how to add other features, such as highlighting current underlying elements while we drag over them. On mouseup – perform all actions related to finishing the drag’n’drop.Then on mousemove move it by changing left/top with position:absolute.On mousedown – prepare the element for moving, if needed (maybe create a clone of it, add a class to it or whatever).The basic Drag’n’Drop algorithm looks like this: So here we’ll see how to implement Drag’n’Drop using mouse events. Also, mobile device support for such events is very weak. And there are many other drag’n’drop tasks that can’t be done using them. Also we can’t make the dragging “horizontal” or “vertical” only. For instance, we can’t prevent dragging from a certain area. Then JavaScript can access the contents of such files.īut native Drag Events also have limitations. These events allow us to support special kinds of drag’n’drop, such as handling dragging a file from OS file-manager and dropping it into the browser window. In the modern HTML standard there’s a section about Drag and Drop with special events such as dragstart, dragend, and so on. Taking something and dragging and dropping it is a clear and simple way to do many things, from copying and moving documents (as in file managers) to ordering (dropping items into a cart). Drag’n’Drop is a great interface solution.