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The error transform works by replacing calls to `invariant` with an `if` statement. Since we're replacing a call expression with a statement, Babel wraps the new statement in an immediately-invoked function expression (IIFE). This wrapper is unnecessary in practice because our `invariant` calls are always part of their own expression statement. In the production bundle, the function wrappers are removed by Closure. But they remain in the development bundles. This commit updates the transform to confirm that an `invariant` call expression's parent node is an expression statement. (If not, it throws a transform error.) Then, it replaces the expression statement instead of the expression itself, effectively removing the extraneous IIFE wrapper.
The error code system substitutes React's error messages with error IDs to provide a better debugging support in production. Check out the blog post here.
codes.jsoncontains the mapping from IDs to error messages. This file is generated by the Gulp plugin and is used by both the Babel plugin and the error decoder page in our documentation. This file is append-only, which means an existing code in the file will never be changed/removed.extract-errors.jsis an node script that traverses our codebase and updatescodes.json. You can test it by runningyarn extract-errors.transform-error-messagesis a Babel pass that rewrites error messages to IDs for a production (minified) build.