Reusable class for loading external script files (e.g. from CDN)

Inject-Script-Example.js

// Example usage of Inject-Script.js

// Example 1: Load a script from an external URL. (preferred method)
// You can call this in a React/Vue/whatever component lifecycle, or wherever.
//  makes sense. Window globals (e.g. `window.YT`) will be available after calling this.
await injectScriptBySrc("https://www.youtube.com/iframe_api", "yt");
// now you can use `window.YT` methods and properties in your code.



// Example 2: Load the raw text content of a script into a page
// You can also call this wherever it makes sense, though it is probably a 
// terrible idea to trigger code this way, and you *should* likely be ashamed.
const myShamefulJS = `
  const something = 1;
  console.log( something );
`
injectScriptContents(myShamefulJS); 
// logs "1" to console after the above line executes.

Inject-Script.js

/**
 * @file Inject-Script
 * @description DYNAMICALLY INJECT EXTERNAL SCRIPT DEPENDENCIES INTO YOUR WEB APP
 *
 * NOTE: Track page-session scripts (i.e. scripts that should be reloaded with the page).
 * You can track as few or as many script dependencies as needed: YouTube is provided as an
 * example below.
 */

// (example for tracking YT script dependency)
let YouTubeLoaded = false; 

// (example if loading Google Charts script into your app)
// let GoogleCharts = false; 

/**
 * Inject a `<script />` tag with the supplied contents into the page's
 * html. This will execute `contents` immediately. You should ideally prefer
 * `injectScriptBySrc( ... )` over this method. If it MUST be used, modify
 * this file to track any required scripts that have to be loaded in this way.
 * @param {string} contents Script tag contents
 */
export function injectScriptContents(contents) {
  const scrpt = document.createElement('script');
  scrpt.innerHTML = contents;
  const lastElem = document.head.lastChild;
  document.head.insertBefore(scrpt, lastElem);

  // Update module state to track that this script has been loaded. e.g.:
  // 
  // YouTubeLoaded = (key === "yt");
  // GoogleChartsLoaded = (key === "gc"); // etc
}

/**
 * Inject a `<script />` tag by `src` attribute into the page's
 * html. This will execute `contents` immediately.
 * @param {string} src External URL for Script source
 * @param {string|undefined} key An internal identifier that helps track whether
 * this script has been loaded in your app (so you don't load it multiple times)
 */
export async function injectScriptBySrc(src, key) {
  // IMPORTANT: Check if script has been loaded; exit if true. For example:
  // if (key === "yt" && YouTubeLoaded) return;

  // Load script from source and inject into page
  const scrpt = document.createElement('script');
  scrpt.src = src;
  scrpt.id = `${key}-script`;
  const lastElem = document.head.lastChild;
  document.head.insertBefore(scrpt, lastElem);

  // Update module state to track that this script has been loaded. e.g.:
  // 
  // YouTubeLoaded = (key === "yt");
  // GoogleChartsLoaded = (key === "gc"); // etc
}

/** 
 * Identify and remove <script /> tag by its id from the page 
 * @param. {string} key Internal identifier for script, so that the module can
 * track its loaded/unloaded status
 */
export function unmountScript(key: string) {
  const id = `${key}-script`;
  const script = document.getElementById(id);
  if (script) script.remove();

  // Update module state to track that this script has been unloaded. e.g.:
  // 
  // switch (key) {
  //   case "gc": return void (GoogleChartsLoaded = false);
  //   case "yt": return void (YouTubeLoaded = false);
  //   default: break;
  // }
}

Public Service Announcement

The gist and example above have been completely changed to reflect my latest approach to this problem.
While I still haven't used react-hot-loader, all comments prior to 2025 are aimed at a previous gist. See revisions for previous versions.