Avoiding Unnecessary Code Download

Thus far, this chapter has mostly discussed strategies for avoiding unnecessary code execution (and that it's not always worth the effort). But it's not just the execution of code that can be an issue. It's also not great if your website visitors have to download lots of code that might never be executed at all. Because every kilobyte of JavaScript code that has to be downloaded will slow down the initial loading time of your web page—not just because of the time it takes to download the code bundle (which can be significant, if users are on a slow network and code bundles are big) but also because the browser has to parse all the downloaded code before your page becomes interactive.

For this reason, a lot of community and ecosystem effort is spent on reducing JavaScript code bundle sizes. Minification (automatic shortening of variable names and other measures to reduce the final code) and compression can help a lot and is...