Convert image to base64 javascript on firefox

I need to convert image that are in a webpage to base64开发者_JAVA百科 over greasemonkey or firefox .xpi extension. How can i do it? I know that i have btoa() function, but i only can use it with strings, not with images. Little help here. Thanks.

You could use the canvas element and draw the image using drawImage() onto it, then use toDataURL() to get the base64 encoded image.

see: https://developer.mozilla.org/en/html/canvas