Element: mousemove event
The mousemove
event is fired at an element when a pointing device (usually a mouse) is moved while the cursor's hotspot is inside it.
Bubbles | Yes |
---|---|
Cancelable | Yes |
Interface | MouseEvent |
Event handler property | onmousemove |
Examples
The following example uses the mousedown
, mousemove
, and mouseup
events to allow the user to draw on an HTML5 canvas. Its functionality is simple: the thickness of the line is set to 1, and the color is always black.
When the page loads, constants myPics
and context
are created to store a reference to the canvas and the 2d context we will use to draw.
Drawing begins when the mousedown
event fires. First we store the x and y coordinates of the mouse pointer in the variables x
and y
, and then set isDrawing
to true.
As the mouse moves over the page, the mousemove
event fires. If isDrawing
is true, the event handler calls the drawLine
function to draw a line from the stored x
and y
values to the current location.
When the drawLine()
function returns, we adjust the coordinates and then save them in x
and y
.
The mouseup
event draws the final line segment, sets x
and y
to 0
, and stops further drawing by setting isDrawing
to false
.
HTML
<h1>Drawing with mouse events</h1>
<canvas id="myPics" width="560" height="360"></canvas>
CSS
canvas {
border: 1px solid black;
width: 560px;
height: 360px;
}
JavaScript
// When true, moving the mouse draws on the canvas
let isDrawing = false;
let x = 0;
let y = 0;
const myPics = document.getElementById('myPics');
const context = myPics.getContext('2d');
// event.offsetX, event.offsetY gives the (x,y) offset from the edge of the canvas.
// Add the event listeners for mousedown, mousemove, and mouseup
myPics.addEventListener('mousedown', e => {
x = e.offsetX;
y = e.offsetY;
isDrawing = true;
});
myPics.addEventListener('mousemove', e => {
if (isDrawing === true) {
drawLine(context, x, y, e.offsetX, e.offsetY);
x = e.offsetX;
y = e.offsetY;
}
});
window.addEventListener('mouseup', e => {
if (isDrawing === true) {
drawLine(context, x, y, e.offsetX, e.offsetY);
x = 0;
y = 0;
isDrawing = false;
}
});
function drawLine(context, x1, y1, x2, y2) {
context.beginPath();
context.strokeStyle = 'black';
context.lineWidth = 1;
context.moveTo(x1, y1);
context.lineTo(x2, y2);
context.stroke();
context.closePath();
}
Result
Specifications
Specification |
---|
UI Events # event-type-mousemove |
Browser compatibility
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