sourcemap-codec

Encode/decode the `mappings` property of a sourcemap.

# Why?

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.

# Installation

npm install sourcemap-codec

# Usage

import { encode, decode } from 'sourcemap-codec';
var decoded = decode( ';EAEEA,EAAE,EAAC,CAAE;ECQY,UACC' );
assert.deepEqual( decoded, [
// the first line (of the generated code) has no mappings,
// as shown by the starting semi-colon (which separates lines)
[],
// the second line contains four (comma-separated) segments
[
// segments are encoded as you'd expect:
// [ generatedCodeColumn, sourceIndex, sourceCodeLine, sourceCodeColumn, nameIndex ]
// i.e. the first segment begins at column 2, and maps back to the second column
// of the second line (both zero-based) of the 0th source, and uses the 0th
// name in the `map.names` array
[ 2, 0, 2, 2, 0 ],
// the remaining segments are 4-length rather than 5-length,
// because they don't map a name
[ 4, 0, 2, 4 ],
[ 6, 0, 2, 5 ],
[ 7, 0, 2, 7 ]
],
// the final line contains two segments
[
[ 2, 1, 10, 19 ],
[ 12, 1, 11, 20 ]
]
]);
var encoded = encode( decoded );
assert.equal( encoded, ';EAEEA,EAAE,EAAC,CAAE;ECQY,UACC' );

# License

MIT