Axe-core file size

[straker]

Below is a table of the sizes of axe.min.js for the last few releases since v3.0.

Release	Minified	Gzipped
3.0.0	236 kB	67.1 kB
3.1.1	284 kB	78.7 kB
3.2.0	318 kB	89.8 kB
3.3.0	342 kB	94.9 kB
3.4.0	405 kB	108 kB
3.5.0	461 kB	126 kB

If we were to release axe-core v4.0 today (which is not feature complete), we would add ~160 kB (~30 kB gzipped) to the minified file size over v3.4.1 which broke Lighthouses budget when they tried to update to it. From v3.5.0, that's an increase of ~90 kb (~12 kB gzipped).

Release	Minified	Gzipped
3.4.0	405 kB	108 kB
3.5.0	461 kB	126 kB
4.0.0	553 kB	138 kB

Once v4.0 is feature complete, we will probably add another another 5 kB gzipped (just a guess). What this means is we've doubled the size of axe-core since releasing the last major release v3.0.

We should figure out some way to at least slow our rate of file size increase, if not figure out a max size we want the library to be.

[WilcoFiers]

I've discussed this with @dylanb, he is on board with introducing the size budget. To address this, I propose we do the following:

1. Before we publish axe-core 4.1, we'll define a size budget for axe-core
2. Every major / minor release, starting with axe-core 4.1 we will reduce the size of axe-core by at least 5kb gzipped since its last major/minor release, until it reaches the size budget.
3. We will put tests in place which will enforce these requirements are met

To reach the size budget, we may decide to create a new .js file from which deprecated features and polyfills are removed. This will be a one-time thing, features deprecated after this file is introduced will be included to avoid breaking changes.

We are looking for input on what would be a preferable maximum GZipped file size for axe-core.

[straker]

I propose we should aim for axe-core to be no larger than 100kB gippzed.

[straker]

Note: I tried switching to terser and didn't see any improvement to our minified / gzip file size using the same options as uglify.

[WilcoFiers]

I'm going to call this done. Axe-core went down from 138k in 4.0 to 108kb in 4.1. We'll still have to define a size budget as per #1930. Pushing that one out to the 4.2 release.