[Dart] Tooltip with Close Delay

See demo first. Move the cursor (mouse pointer) to hover over the blue text with underline:


If the cursor leaves the blue text and does not enter the tooltip within 250ms, the tooltip will be closed. If the cursor leaves the blue text and is in the tooltip after 250ms, the tooltip will still be visible without being closed.

The demo here is not the same as the implementation of simple tooltip in my previous post [2]. In my previous post, the tooltip will be closed right after the cursor leaves the blue text without any delay.

To achieve the effect of the demo, first wrap the text with proper HTML tag. In the example of demo, we wrap the text tooltip and Dart with span tag. Then put the explanation of the text in the data-descr attribute of the tag, just like the following HTML code used in the demo:


This is a <span data-descr="hello, I am tooltip!">tooltip</span> example via
<span data-descr="programming language from Google">Dart</span>.

Next, add the following rules to your CSS code:


*[data-descr] {
  text-decoration: underline;
  color: blue;
  cursor: help;

.invisible {
  display: none;

.tooltip {
  position: absolute;
  border: 1px gray solid;
  border-radius: 3px;
  padding: 3px;
  1. First rule says add underline to the text wrapped in the element with data-descr attribute, make the text blue, and make the mouse cursor become help icon on hover over.
  2. Second rule, as the name suggests, is used to make element invisible.
  3. Third rule is used to style the tooltip box that shows the description of the text.

Then add the following to your Dart code:


import 'dart:html';
import 'dart:async';

DivElement tooltip;

// indicate if the mouse cursor is in the tooltip
bool isCursorInTooltip = false;

// when cursor leaves the text, the delay time to close the tooltip if the
// cursor is not in the tooltip. (milisecond)
const delay = const Duration(milliseconds: 250);

// event handler for mouseenter event of elements with data-descr attribute
void ShowTooltip(Event e) {
  Element elm = e.target;
  tooltip.style.left = elm.offsetLeft.toString() + "px";
  tooltip.style.top = (elm.offsetTop + elm.offsetHeight + 5).toString() + "px";
  tooltip.text = elm.dataset["descr"];

// event handler for mouseleave event of elements with data-descr attribute
void HideTooltip(Event e) {
  new Timer(delay, () {
    if (!isCursorInTooltip) {

void main() {
  // create and append invisible tooltip to DOM tree
  tooltip = document.createElement("div");
  tooltip.onMouseEnter.listen((Event e) {
    isCursorInTooltip = true;
  tooltip.onMouseLeave.listen((Event e) {
    isCursorInTooltip = false;

  // select all elements with data-descr attribute
  // and attach mouseenter and mouseleave event handler
  var els = querySelectorAll('*[data-descr]');
  for (var el in els) {

In the Dart code:

  1. Create and append a tooltip (div element) to the HTML body. The tooltip is used to show description on mouse hovering over the text. The tooltip is invisible in the beginning.
  2. Attach mouseenter and mouseleave event handler to the tooltip. In the event handler, set the variable isCursorInTooltip accordingly. Also close the tooltip if the cursor leaves the tooltip.
  3. Define mouseenter and mouseleave event handler to texts wrapped in the element with data-descr attribute. In mouseenter handler we show the description of the text in the tooltip, and in mouseleave handler we make the tooltip invisible if the cursor is not in the tooltip after 250ms.
  4. Use querySelectorAll to find all elements with data-descr attribute, and attach corresponding mouseenter/mouseleave event handlder to show/hide description of texts.

This post is actually the Dart translation of JavaScript implememtation [1].

Tested on: DartPad.


[1][JavaScript] Tooltip with Close Delay
[2][Dart] Tooltip
[3]How do I do the equivalent of setTimeout + clearTimeout in Dart? - Stack Overflow