The UI Events API defines a system for handling user interactions such as mouse and keyboard input. This includes:
- events that are fired on specific user actions such keypresses or mouse clicks. Most of these events fire on the
Element interface, but the events relating to loading and unloading resources fire on the Window interface. - event interfaces, which are passed into handlers for these events. These interfaces inherit from
Event and provide extra information specific to the type of user interaction: for example, the KeyboardEvent is passed into a keydown event handler and provides information about the key that was pressed.
This example logs mouse events along with the X and Y coordinates at which the event was generated. Try moving the mouse into the yellow and red squares, and clicking or double-clicking.
HTML
<div id="outer">
<div id="inner"></div>
</div>
<div id="log">
<pre id="contents"></pre>
<button id="clear">Clear log</button>
</div>
CSS
body {
display: flex;
gap: 1rem;
}
#outer {
height: 200px;
width: 200px;
display: flex;
justify-content: center;
align-items: center;
background-color: yellow;
}
#inner {
height: 100px;
width: 100px;
background-color: red;
}
#contents {
height: 150px;
width: 250px;
border: 1px solid black;
padding: 0.5rem;
overflow: scroll;
}
JavaScript
const outer = document.querySelector("#outer");
const inner = document.querySelector("#inner");
const contents = document.querySelector("#contents");
const clear = document.querySelector("#clear");
let lines = 0;
outer.addEventListener("click", (event) => {
log(event);
});
outer.addEventListener("dblclick", (event) => {
log(event);
});
outer.addEventListener("mouseover", (event) => {
log(event);
});
outer.addEventListener("mouseout", (event) => {
log(event);
});
outer.addEventListener("mouseenter", (event) => {
log(event);
});
outer.addEventListener("mouseleave", (event) => {
log(event);
});
function log(event) {
const prefix = `${String(lines++).padStart(3, "0")}: `;
const line = `${event.type}(${event.clientX}, ${event.clientY})`;
contents.textContent = `${contents.textContent}${prefix}${line}\n`;
contents.scrollTop = contents.scrollHeight;
}
clear.addEventListener("click", () => {
contents.textContent = "";
lines = 0;
});
Result
This example logs keydown, beforeinput and, input events. Try typing into the text area. Note that keys like Shift produce keydown events but not input events.
HTML
<textarea id="story" rows="5" cols="33"></textarea>
<div id="log">
<pre id="contents"></pre>
<button id="clear">Clear log</button>
</div>
CSS
body {
display: flex;
gap: 1rem;
}
#story {
padding: 0.5rem;
}
#contents {
height: 150px;
width: 250px;
border: 1px solid black;
padding: 0.5rem;
overflow: scroll;
}
JavaScript
const story = document.querySelector("#story");
const contents = document.querySelector("#contents");
const clear = document.querySelector("#clear");
let lines = 0;
story.addEventListener("keydown", (event) => {
log(`${event.type}(${event.key})`);
});
story.addEventListener("beforeinput", (event) => {
log(`${event.type}(${event.data})`);
});
story.addEventListener("input", (event) => {
log(`${event.type}(${event.data})`);
});
function log(line) {
const prefix = `${String(lines++).padStart(3, "0")}: `;
contents.textContent = `${contents.textContent}${prefix}${line}\n`;
contents.scrollTop = contents.scrollHeight;
}
clear.addEventListener("click", () => {
contents.textContent = "";
lines = 0;
});
Result