merge-source-map

What is merge-source-map?

The merge-source-map npm package is a utility that allows developers to merge multiple source maps. This is particularly useful in development environments where JavaScript files are transformed through processes like minification or transpilation, and maintaining accurate source maps is crucial for debugging.

What are merge-source-map's main functionalities?

Merge Source Maps

This feature allows the merging of two source maps into one. It is useful when you have transformations applied in stages and need to track the original source accurately across these transformations.

const mergeSourceMap = require('merge-source-map');
const originalMap = { version: 3, sources: ['foo.js'], names: [], mappings: 'AAAA' };
const additionalMap = { version: 3, sources: ['foo.js'], names: [], mappings: 'CAAC' };
const mergedMap = mergeSourceMap(originalMap, additionalMap);
console.log(mergedMap);

Other packages similar to merge-source-map

source-map

The 'source-map' package provides functionalities for generating and consuming source maps. It can be used to manipulate and merge source maps similarly to 'merge-source-map', but it also includes features for creating new source maps from scratch, which 'merge-source-map' does not offer.

combine-source-map

Similar to 'merge-source-map', 'combine-source-map' allows for the combination of multiple source maps into a single map. It is particularly useful in browserify chains. The main difference is that 'combine-source-map' focuses more on integration with browserify, whereas 'merge-source-map' is more general-purpose.

README

merge-source-map

Merge old source map and new source map in multi-transform flow

API

var merge = require('merge-source-map')

merge(oldMap, newMap)

Merge old source map and new source map and return merged. If old or new source map value is falsy, return another one as it is.

oldMap : object|undefined

old source map object

newmap : object|undefined

new source map object

Example

var esprima    = require('esprima'),
    estraverse = require('estraverse'),
    escodegen  = require('escodegen'),
    convert    = require('convert-source-map'),
    merge      = require('merge-source-map')

const CODE = 'a = 1',
      FILEPATH = 'a.js'

// create AST of original code
var ast = esprima.parse(CODE, {sourceType: 'module', loc: true})

// transform AST of original code
estraverse.replace(ast, {
  enter: function(node, parent) { /* change AST */ },
  leave: function(node, parent) { /* change AST */ }
})

// generate code and source map from transformed AST
var gen = escodegen.generate(ast, {
  sourceMap: FILEPATH,
  sourceMapWithCode: true,
  sourceContent: CODE
})

// merge old source map and new source map
var oldMap = convert.fromSource(CODE) && convert.fromSource(CODE).toObject(),
    newMap = JSON.parse(gen.map.toString()),
    mergedMap = merge(oldMap, newMap),
    mapComment = convert.fromObject(mergedMap).toComment()

// attach merge source map to transformed code
var transformed = gen.code + '\n' + mapComment

console.log(transformed);

Test

% npm install
% npm test

License

MIT (c) keik