@babel/plugin-transform-block-scoping 做了什么不是 babel 核心行为的一部分？

Question

The docs leave a lot to be desired, as is sometimes the case with Babel plugins.

This plugin also validates all const variables. Reassignment of constants is a runtime error and it will insert the necessary error code for those.

I don't know what this means? Isn't that always going to cause a runtime error?

And the example it provides only uses let and var which furthers my confusion.

Answer 1

In es5, const does not exist. If you are compiling your code down to es5, all your const declarations will become var declarations. The plugin will insert runtime code for the const values to throw an error if they are assigned a new value, likely by converting references to accessor function calls.