How does @babel/preset-env transpile the JS code based on Browserslist?

[mrdulin]

For example, the "chrome: 49" query. My understand is babel will transpiled the JS code compatible with Chrome 49 version.

How does @babel/preset-env know what kind of transpiled JS code should be emited? What babel plugin, polyfill should be used?

The query is very fragmented, and it seems impossible to use a mapping of query and plugins, so babel can get the needed plugins by query.

For example：

• babel will include plugin-a, plugin-b, polyfill-a, polyfill-b for "chrome 49" query.
• babel will include plugin-a, polyfill-a for "chrome 86" query.

I didn't find the source code or any doc explain this process.

[ai]

You should ask Babel. We only transpile high level queries like last 2 versions to exact list of versions.

But as I know they use some database of version>feature.

[mrdulin]

Can you explain "transpile high level queries like last 2 versions to exact list of versions."

What's the exact list of versions?