Re-port the JS repo

[adil192]

• Discussed in https://github.com/steveruizok/perfect-freehand-dart/issues/10
• Please make sure that you're happy with how you're credited in the README
• We'll need to make sure the GitHub Pages demo works properly after merging

[steveruizok]

Looks great! Merging in now. Thanks so much for the work!