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Nodes

Every node in the TS AST has an optional emitNode, this node provides a sort of wrapping context to a node when it is emitted. For example it keeps track of trailing/leading comments and importantly for sourcemaps: sourceMapRange and tokenSourceMapRange.

These are applied via code transformers in TypeScript

Creating the Files

Files are created inside emitter.ts - the opening function being emitWorker.

  • Each source file then gets writeFile called on it which triggers the AST traversal on the source file
  • A sourceMapGenerator is created
  • Each node gets triggered via pipelineEmit
    • pipelineEmit runs all transformers against the node
    • This is where the pipeline-ing for TS -> ES2020 -> ES2018 -> ES2017 -> ES2015 -> ES6 happens to that node
    • Each node calls emitSourcePos which tells the sourceMapGenerator that a mapping exists for this node

This means when looking into how TS handles sourcemap, you need to find the part of the above pipeline which transforms the syntax you're looking for.