I played around with tf.js a few weeks ago and learning to use python-trained models was the first hurdle. I made a minimal working example of this here, feel free to check it out:

https://github.com/paruby/mnist

See model/mnist_js.ipynb to see how the model is trained and exported to a js readable format, and you can see in lines 13-15 in index.html how the model is loaded.

Note: I have a decent amount of ML experience but almost no javascript experience, so YMMV