@segment/load-script/index.js

Dynamically and asynchronously load a script file.

'use strict';

/*
 * Module dependencies.
 */

var onload = require('script-onload');
var tick = require('next-tick');
var type = require('component-type');

/**
 * Loads a script asynchronously.
 *
 * @param {Object} options
 * @param {Function} cb
 */
function loadScript(options, cb) {
  if (!options) {
    throw new Error('Can\'t load nothing...');
  }

  // Allow for the simplest case, just passing a `src` string.
  if (type(options) === 'string') {
    options = { src : options };
  }

  var https = document.location.protocol === 'https:' || document.location.protocol === 'chrome-extension:';

  // If you use protocol relative URLs, third-party scripts like Google
  // Analytics break when testing with `file:` so this fixes that.
  if (options.src && options.src.indexOf('//') === 0) {
    options.src = (https ? 'https:' : 'http:') + options.src;
  }

  // Allow them to pass in different URLs depending on the protocol.
  if (https && options.https) {
    options.src = options.https;
  } else if (!https && options.http) {
    options.src = options.http;
  }

  // Make the `<script>` element and insert it before the first script on the
  // page, which is guaranteed to exist since this Javascript is running.
  var script = document.createElement('script');
  script.type = 'text/javascript';
  script.async = true;
  script.src = options.src;

  // If we have a cb, attach event handlers. Does not work on < IE9 because
  // older browser versions don't register element.onerror
  if (type(cb) === 'function') {
    onload(script, cb);
  }

  tick(function() {
    // Append after event listeners are attached for IE.
    var firstScript = document.getElementsByTagName('script')[0];
    firstScript.parentNode.insertBefore(script, firstScript);
  });

  // Return the script element in case they want to do anything special, like
  // give it an ID or attributes.
  return script;
}

/*
 * Exports.
 */

module.exports = loadScript;