The non-standard HTMLCanvasElement.mozOpaque property is a boolean value reflecting the moz-opaque HTML attribute of the <canvas> element. It lets the canvas know whether or not translucency will be a factor. If the canvas knows there's no translucency, painting performance can be optimized.

A boolean value.

Given this <canvas> element:

<canvas id="canvas" width="300" height="300" moz-opaque></canvas>

You can get or set the mozOpaque property. For example, you could conditionally set it to true if mimeType === 'image/jpeg', or similar, to gain performance in your application when translucency is not needed.

const canvas = document.getElementById("canvas");
console.log(canvas.mozOpaque); // true
// deactivate it
canvas.mozOpaque = false;

Not part of any standard.

• HTMLCanvasElement: Interface used to define the HTMLCanvasElement.mozOpaque property
• moz-opaque: HTML attribute of the <canvas> element
• Optimizing your JavaScript game for Firefox OS