The CanvasRenderingContext2D.clearRect()
method of the Canvas 2D API erases the pixels in a rectangular area by setting them to transparent black.
Note: Be aware that clearRect()
may cause unintended side effects if you're not using paths properly. Make sure to call beginPath()
before starting to draw new items after calling clearRect()
.
clearRect(x, y, width, height)
The clearRect()
method sets the pixels in a rectangular area to transparent black (rgba(0,0,0,0)
). The rectangle's top-left corner is at (x, y)
, and its size is specified by width
and height
.
This code snippet erases the entire canvas. This is commonly required at the start of each frame in an animation. The dimensions of the cleared area are set to equal the <canvas>
element's width
and height
attributes.
const canvas = document.getElementById("canvas");
const ctx = canvas.getContext("2d");
ctx.clearRect(0, 0, canvas.width, canvas.height);
This example draws a blue triangle on top of a yellowish background. The clearRect()
method then erases part of the canvas.
HTML
<canvas id="canvas"></canvas>
JavaScript
The cleared area is rectangular in shape, with its top-left corner at (10, 10). The cleared area has a width of 120 and a height of 100.
const canvas = document.getElementById("canvas");
const ctx = canvas.getContext("2d");
ctx.beginPath();
ctx.fillStyle = "#ff6";
ctx.fillRect(0, 0, canvas.width, canvas.height);
ctx.beginPath();
ctx.fillStyle = "blue";
ctx.moveTo(20, 20);
ctx.lineTo(180, 20);
ctx.lineTo(130, 130);
ctx.closePath();
ctx.fill();
ctx.clearRect(10, 10, 120, 100);
Result