So incase you havn't been following me. I joined Cargurus in July. At cargurus we're currently working on our mobile web experience written in react, redux and reselect. As our implementation grew so did our time to first paint.
You get started by
npm install -g source-map-explorer then just download your bundles, and sourcemaps. You can do this from production if you have them. Otherwise build bundles locally. Note You should always use this on minified code where any tree shaking and dead code elimination has occurred. In the command line run
source-map-explorer ./yourbundle.js ./yourbundle.js.map Your browser should then open with a great tree view of what is inside your bundle. From here you can look to see what dependencies you have, and their sizes. Obviously, you can then decide to keep or throw them away.
Here is a great youtube video explaining it in detail!