The Inner Workings of JavaScript Source Maps

Source maps enable debugging of minified JavaScript by mapping production code back to original sources. This technical exploration covers the source map JSON format, the VLQ (Variable Length Quantity) encoding scheme used in the mappings field, and how position data is compressed using Base64 characters. The article walks through the TypeScript build pipeline stages and demonstrates how segments encode relative position differences between generated and source files, explaining why this compression method keeps source map files manageable in size.