Nice! I had fun with this, especially comparing Ember's half a meg footprint to Backbone's 20K. One helpful data point could be whether the library supports a (formal) custom build apparatus, since you can often get a sizable reduction that way. Full jQuery UI clocks in at ~242K, but using http://jqueryui.com/download/ you can often strip it down to 20K or less. Similarly with THREE.js and several others. Going in the other direction, a library that seems small (Backbone.js, @ ~20K) may actually end up being relatively heavy because of required external dependencies. A more explicit side-by-side "compare" function would also be nice here, comparing library size along with other metrics like script loader compatibility, maintenance frequency, different flavors of popularity, etc.