Source maps are the main piece in the jigsaw puzzle of mapping symbols and locations from "built" JavaScript files back to the original source code. When you debug minified JavaScript in your browser's DevTools and see the original source with proper variable names and formatting, you're witnessing source maps in action.
For example, when your browser encounters an error at bundle.min.js:1:27698 , the source map translates this to src/index.ts:73:16 , revealing exactly where the issue occurred in your original TypeScript code:
Production Bundle bundle.min.js:1:27698 Source Map Lookup Original Source Location src/index.ts:73:16 Production Bundle bundle.min.js:1:27698 Source Map Lookup Original Source Location src/index.ts:73:16
But how does this actually work under the hood? In this post, we'll take a deep dive into the internals of source maps, exploring their format, encoding mechanisms, and how devtools use them to bridge the gap between production code and developer-friendly sources.
The TypeScript Build Pipeline
Modern JavaScript builds typically involve three main stages:
Transpilation : TypeScript → JavaScript
: TypeScript → JavaScript Bundling : Combining modules into a single file
: Combining modules into a single file Minification: Compressing code for production
At each stage, source maps preserve the connection back to the original code.
... continue reading