React, performance and -500 milliseconds at launch - the history of our optimizations in numbers

Let's get a little distracted from the coronavirus, and talk about something technical. For example, about how we tried to improve the cold start time of one react application and what came of it. Who cares about the topic of performance and fast web as a whole - please, under cat. At the end there will be a small survey about the price / need for such optimizations.

First, a little context. Usually we make different banking applications, which are mostly not accessible to the general public. But recently a small miracle happened and we were given the task of writing a public application (let's say, almost public). Of the basic requirements, only mobile-first, react, and IE can not be supported (even 11). Of the features - a one-time app (i.e., the user does not go there more often than once a year) and without data the application is absolutely and completely useless. It is useless to such an extent that we cannot even show a footer, because we don’t know in what color to show it and what to write there at all.

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