Prepend empty lines to existing source-map

prepend-empty-lines.js

#!/usr/bin/env node
const sourceMap = require('source-map')
const fs = require('fs')
const path = require('path')

/**
 * Prepend six lines to source-map
 */
const runSourceMapPrepend = async (sourceMapFile) => {
  const sourceMapFileContent = fs.readFileSync(sourceMapFile, 'utf8')
  const originalConsumer = await new sourceMap.SourceMapConsumer(
    sourceMapFileContent,
  )

  const node = sourceMap.SourceNode.fromStringWithSourceMap(
    sourceMapFileContent,
    await new sourceMap.SourceMapConsumer(sourceMapFileContent),
  )
  // add six empty lines
  node.prepend('\n\n\n\n\n')
  const newConsumer = sourceMap.SourceNode.fromStringWithSourceMap(
    sourceMapFileContent,
    originalConsumer,
  )
  const generator = sourceMap.SourceMapGenerator.fromSourceMap(originalConsumer)

  const newSourceMapFileName = 'prepended-' + path.basename(sourceMapFile)
  fs.writeFileSync(newSourceMapFileName, generator.toString())
  console.log(
    'Prepended 6 empty lines to source-map. Written to: ' +
      newSourceMapFileName,
  )
}

const fileSource = process.argv[2]
if (!fileSource) {
  throw Error('No source for source-map-file given!')
}

runSourceMapPrepend(fileSource)