sourcemap-codec

What is sourcemap-codec?

The sourcemap-codec npm package is designed for encoding and decoding mappings between original and generated code as represented in a source map. It provides efficient operations for working with the VLQ (Variable-Length Quantity) encoding used in source maps, making it easier to manipulate and understand the relationships between source and transformed code.

What are sourcemap-codec's main functionalities?

Encoding source map mappings

This feature allows you to encode an array of source map mappings into a compact string using VLQ encoding. The example demonstrates encoding mappings for two lines of code.

const { encode } = require('sourcemap-codec');
const mappings = [
  [ [ 0, 0, 0, 0 ], [ 1, 0, 1, 17 ] ], // First line mappings
  [ [ 0, 0, 1, 0 ] ] // Second line mappings
];
const encodedMappings = encode(mappings);

Decoding source map mappings

This feature enables the decoding of a VLQ-encoded string representing source map mappings back into a more understandable array format. The example shows how to decode a string into mappings for two lines.

const { decode } = require('sourcemap-codec');
const encodedMappings = 'AAAA,CAAC;AACA';
const mappings = decode(encodedMappings);

Other packages similar to sourcemap-codec

source-map

The source-map package provides functionalities to generate and consume source maps. It offers a more comprehensive set of features compared to sourcemap-codec, including the ability to add and retrieve mappings, but it might be heavier for projects only needing encoding and decoding.

source-map-js

source-map-js is a fork of the original source-map library, intended to provide similar functionalities with some performance improvements and bug fixes. Like source-map, it is more feature-rich but also more complex than sourcemap-codec.

README

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

Changelog

1.4.8

• Performance boost (#80)