myapp/node_modules/webpack-dev-middleware/lib/context.js

'use strict';

const weblog = require('webpack-log');

module.exports = function ctx(compiler, options) {
  const context = {
    state: false,
    webpackStats: null,
    callbacks: [],
    options,
    compiler,
    watching: null,
    forceRebuild: false,
  };

  if (options.logger) {
    context.log = options.logger;
  } else {
    context.log = weblog({
      level: options.logLevel || 'info',
      name: 'wdm',
      timestamp: options.logTime,
    });
  }

  const { log } = context;

  function done(stats) {
    // We are now on valid state
    context.state = true;
    context.webpackStats = stats;

    // Do the stuff in nextTick, because bundle may be invalidated
    // if a change happened while compiling
    process.nextTick(() => {
      // check if still in valid state
      if (!context.state) {
        return;
      }

      // print webpack output
      context.options.reporter(context.options, {
        log,
        state: true,
        stats,
      });

      // execute callback that are delayed
      const cbs = context.callbacks;
      context.callbacks = [];
      cbs.forEach((cb) => {
        cb(stats);
      });
    });

    // In lazy mode, we may issue another rebuild
    if (context.forceRebuild) {
      context.forceRebuild = false;
      rebuild();
    }
  }

  function invalid(callback) {
    if (context.state) {
      context.options.reporter(context.options, {
        log,
        state: false,
      });
    }

    // We are now in invalid state
    context.state = false;
    if (typeof callback === 'function') {
      callback();
    }
  }

  function rebuild() {
    if (context.state) {
      context.state = false;
      context.compiler.run((err) => {
        if (err) {
          log.error(err.stack || err);
          if (err.details) {
            log.error(err.details);
          }
        }
      });
    } else {
      context.forceRebuild = true;
    }
  }

  context.rebuild = rebuild;
  context.compiler.hooks.invalid.tap('WebpackDevMiddleware', invalid);
  context.compiler.hooks.run.tap('WebpackDevMiddleware', invalid);
  context.compiler.hooks.done.tap('WebpackDevMiddleware', done);
  context.compiler.hooks.watchRun.tap(
    'WebpackDevMiddleware',
    (comp, callback) => {
      invalid(callback);
    }
  );

  return context;
};