smallest-script-loader/dist/index.js

Smallest promise-based script loader with cache support

(function (global, factory) {
  if (typeof define === "function" && define.amd) {
    define(['exports'], factory);
  } else if (typeof exports !== "undefined") {
    factory(exports);
  } else {
    var mod = {
      exports: {}
    };
    factory(mod.exports);
    global.index = mod.exports;
  }
})(this, function (exports) {
  'use strict';

  Object.defineProperty(exports, "__esModule", {
    value: true
  });
  exports.default = loadScript;
  const scripts = new Map();

  /**
   * Loads an external script
   * @param {string} url Script's URL
   * @returns {Promise}
   */
  function loadScript(url) {
    if (scripts.has(url)) {
      return scripts.get(url);
    }

    const script = document.createElement('script');
    script.async = true;

    scripts.set(url, new Promise(function (resolve, reject) {
      script.addEventListener('load', resolve);
      script.addEventListener('error', () => reject(new Error(`Failed to load the script: ${url}.`)));
      script.src = url;
      document.body.appendChild(script);
    }));

    return scripts.get(url);
  }
});