by Rich-Harris

Rich-Harris / sorcery

Resolve a chain of sourcemaps back to the original source, like magic

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Sourcemaps are great - if you have a JavaScript file, and you minify it, your minifier can generate a map that lets you debug as though you were looking at the original uncompressed code.

But if you have more than one transformation - say you want to transpile your JavaScript, concatenate several files into one, and minify the result - it gets a little trickier. Each intermediate step needs to be able to both ingest a sourcemap and generate one, all the time pointing back to the original source.

Most compilers don't do that. (UglifyJS is an honourable exception.) So when you fire up devtools, instead of looking at the original source you find yourself looking at the final intermediate step in the chain of transformations.

Sorcery aims to fix that. Given an file at the end of a transformation chain (e.g., your minified JavaScript), it will follow the entire chain back to the original source, and generate a new sourcemap that describes the whole process. How? Magic.

This is a work-in-progress - suitable for playing around with, but don't rely on it to debug air traffic control software or medical equipment. Other than that, it can't do much harm.


As a node module

Install sorcery locally:

npm install sorcery
var sorcery = require( 'sorcery' );

sorcery.load( 'some/generated/code.min.js' ).then( function ( chain ) { // generate a flattened sourcemap var map = chain.apply(); // { version: 3, file: 'code.min.js', ... }

// get a JSON representation of the sourcemap map.toString(); // '{"version":3,"file":"code.min.js",...}'

// get a data URI representation map.toUrl(); // 'data:application/json;charset=utf-8;base64,eyJ2ZXJ...'

// write to a new file - this will create output.js and //, and will preserve relative paths. It // returns a Promise chain.write( 'output.js' );

// write to a new file but use an absolute path for the // sourceMappingURL chain.write( 'output.js', { absolutePath: true });

// write to a new file, but append the flattened sourcemap as a data URI chain.write( 'output.js', { inline: true });

// overwrite the existing file chain.write(); chain.write({ inline: true });

// find the origin of line x, column y. Returns an object with // source, line, column and (if applicable) name properties. // Note - for consistency with other tools, line numbers are always // one-based, column numbers are always zero-based. It's daft, I know. var loc = chain.trace( x, y ); });

// You can also use sorcery synchronously: var chain = sorcery.loadSync( 'some/generated/code.min.js' ); var map = chain.apply(); var loc = chain.trace( x, y ); chain.writeSync();

Advanced options

You can pass an optional second argument to

, with zero or more of the following properties:
  • content
    - a map of
    filename: contents
    will be resolved against the current working directory if needs be
  • sourcemaps
    - a map of
    filename: sourcemap
    pairs, where
    is the name of the file the sourcemap is related to. This will override any
    comments in the file itself.

For example:

sorcery.load( 'some/generated/code.min.js', {
  content: {
    'some/minified/code.min.js': '...',
    'some/transpiled/code.js': '...',
    'some/original/code.js': '...'
  sourcemaps: {
    'some/minified/code.min.js': {...},
    'some/transpiled/code.js': {...}
}).then( chain => {
  /* ... */

Any files not found will be read from the filesystem as normal.

On the command line

First, install sorcery globally:

npm install -g sorcery
  sorcery [options]

Options: -h, --help Show help message -v, --version Show version -i, --input Input file -o, --output Output file (if absent, will overwrite input) -d, --datauri Append map as a data URI, rather than separate file -x, --excludeContent Don't populate the sourcesContent array


# overwrite sourcemap in place (will write map to
# some/generated/, and update
# sourceMappingURL comment if necessary
sorcery -i some/generated/code.min.js

append flattened sourcemap as an inline data URI

(will delete existing .map file, if applicable)

sorcery -d -i some/generated/code.min.js

write to a new file (will create newfile.js and

sorcery -i some/generated/code.min.js -o newfile.js



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