>and that works.
Depends on the browser. IE > 8 doesn't support it.
Are you saying processing.js doesn't work in IE after IE 8?
IE 8 and above only supports image data URIs within CSS, link and image tags[0]. Processing.js probably works around that with Canvas or something.
[0]https://developer.mozilla.org/en-US/docs/Web/HTTP/data_URIs
There are also clumsier ways to draw lines, like with DOM manipulation in SVG or drawing stuff on a <canvas>, and those might be desirable for the extra flexibility they give you. But you don't have to start with them.