Custom HTML Element for selecting percentages.
Include <script src="piechartinput.js"></script> in the body of your html file.
The tag is <pie-input>, and the available attributes are size (in pixels), value (comma-separated list), initial-angle (in radians), colors (comma-separated list), line-thickness (in pixels), handle-radius (in pixels), and onchange (function name string).
Example:
<pie-input size="300" values=".25, .45, .3" initial-angle="3.14" colors="red, blue, #00FF00" line-thickness="10" handle-radius="15"></pie-input>
The value attribute is updated every time the values change, so they can be accessed with
document.querySelector('pie-input').getAttribute('value')
However, it is advisable to use an onchange function. See demo.html for an example.