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"Smart" tooltip

importance: 5

Write a function that shows a tooltip over an element only if the visitor moves the mouse over it, but not through it.

In other words, if the visitor moves the mouse on the element and stopped – show the tooltip. And if they just moved the mouse through fast, then no need, who wants extra blinking?

Technically, we can measure the mouse speed over the element, and if it’s slow then we assume that it comes “over the element” and show the tooltip, if it’s fast – then we ignore it.

Make a universal object new HoverIntent(options) for it. With options:

  • elem – element to track.
  • over – a function to call if the mouse is slowly moving over the element.
  • out – a function to call when the mouse leaves the element (if over was called).

An example of using such object for the tooltip:

// a sample tooltip
let tooltip = document.createElement('div');
tooltip.className = "tooltip";
tooltip.innerHTML = "Tooltip";

// the object will track mouse and call over/out
new HoverIntent({
  over() { = elem.getBoundingClientRect().left + 'px'; = elem.getBoundingClientRect().bottom + 5 + 'px';
  out() {

The demo:

If you move the mouse over the “clock” fast then nothing happens, and if you do it slow or stop on them, then there will be a tooltip.

Please note: the tooltip doesn’t “blink” when the cursor moves between the clock subelements.

Open a sandbox with tests.

The algorithm looks simple:

  1. Put onmouseover/out handlers on the element. Also can use onmouseenter/leave here, but they are less universal, won’t work if we introduce delegation.
  2. When a mouse cursor entered the element, start measuring the speed on mousemove.
  3. If the speed is slow, then run over.
  4. Later if we’re out of the element, and over was executed, run out.

The question is: “How to measure the speed?”

The first idea would be: to run our function every 100ms and measure the distance between previous and new coordinates. If it’s small, then the speed is small.

Unfortunately, there’s no way to get “current mouse coordinates” in JavaScript. There’s no function like getCurrentMouseCoordinates().

The only way to get coordinates is to listen to mouse events, like mousemove.

So we can set a handler on mousemove to track coordinates and remember them. Then we can compare them, once per 100ms.

P.S. Please note: the solution tests use dispatchEvent to see if the tooltip works right.

Open the solution with tests in a sandbox.