HTML5 Canvas Cookbook

Appendix A. Detecting Canvas Support

Canvas fallback content

As all the browsers do not support canvas, it's a good idea to provide fallback content so that the users know that something isn't working correctly in the event that their browser of choice does not support canvas. The simplest and most straightforward technique for handling browsers that don't support canvas is to add fallback content inside of the canvas tag. Typically, this content will be text or an image that tells the user that their outdated browser doesn't support canvas, followed by a suggestion for downloading a browser developed in this decade. Users who are using a browser that does support canvas will not see the inner content:

<canvas id="myCanvas" width="578" height="250"> ...