mappings property of a sourcemap.
Sourcemaps are difficult to generate and manipulate, because the
mappings property – the part that actually links the generated code back to the original source – is encoded using an obscure method called Variable-length quantity. On top of that, each segment in the mapping contains offsets rather than absolute indices, which means that you can't look at a segment in isolation – you have to understand the whole sourcemap.
This package makes the process slightly easier.
npm install sourcemap-codec
;var decoded = ;assert;var encoded = ;assert;