universal-webpack/es6/waitForFile.js

Isomorphic Webpack

import fs from 'fs'; // Waits for a file to be created
// (e.g. after Webpack build process finishes).
//
// The Promise is resolved when the file has been found
// (for example, this is needed for development because
//  `webpack-dev-server` and Node.js application server
//  are run in parallel).
//

export default function wait_for_file(path) {
  // waits for condition to be met, then resolves the promise
  return new Promise(function (resolve) {
    var tick_interval = 300; // show the message not too often

    var message_timer = 0;
    var message_interval = 2000; // in milliseconds

    tick(function () {
      // Check if the file exists in the filesystem
      var exists = fs.existsSync(path);

      if (!exists) {
        return false;
      } // Check if the file contents have been written to disk
      // https://github.com/catamphetamine/universal-webpack/issues/24


      var contents = fs.readFileSync(path, 'utf8'); // Check if the file contents is empty

      if (!contents) {
        return false;
      }

      return true;
    }, tick_interval, resolve, function () {
      message_timer += tick_interval;

      if (message_timer >= message_interval) {
        message_timer = 0;
        console.log("(\"".concat(path, "\" not found)"));
        console.log('(waiting for the file to be generated; e.g. as a result of a Webpack build)');
      }
    });
  });
}

function tick(check_condition, interval, done, not_done_yet) {
  var condition_is_met = check_condition();

  if (condition_is_met) {
    return done();
  }

  not_done_yet();
  setTimeout(function () {
    return tick(check_condition, interval, done, not_done_yet);
  }, interval);
}
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