create-js-app-scripts/node_modules/assets-webpack-plugin/lib/output/createOutputWriter.js

Configuration and scripts for Create Js App.

var mkdirp = require('mkdirp');
var path = require('path');
var fs = require('fs');
var merge = require('lodash.merge');

var error = require('../utils/error');


module.exports = function (options) {
  var outputPath = path.join(options.path, options.filename);
  var update = options.update;
  var firstRun = true;

  options.processOutput = options.processOutput || function (assets) {
    return JSON.stringify(assets, null, options.prettyPrint ? 2 : null);
  };

  return function writeOutput (newAssets, next) {
        // if potions.update is false and we're on the first pass of a (possibly) multicompiler
    var overwrite = !update && firstRun;

    mkdirp(options.path, function (err) {
      if (err) {
        return next(error('Could not create output folder ' + options.path, err));
      }
      fs.readFile(outputPath, 'utf8', function (err, data) {
                // if file does not exist, just write data to it
        if (err && err.code !== 'ENOENT') {
          return next(error('Could not read output file ' + outputPath, err));
        }
                // if options.update is false and we're on first run,
                // start with empty data
        data = overwrite ? '{}' : data || '{}';

        var oldAssets;
        try {
          oldAssets = JSON.parse(data);
        } catch (err) {
          oldAssets = {};
        }

        var assets = merge({}, oldAssets, newAssets);
        var output = options.processOutput(assets);
        if (output !== data) {
          fs.writeFile(outputPath, output, function (err) {
            if (err) {
              return next(error('Unable to write to ' + outputPath, err));
            }
            firstRun = false;
            next();
          });
        } else {
          next();
        }
      });
    });
  };
};