add-javascript 📜

Just add JavaScript.

Includes validation, integrity checking, caching, and a cross-framework hook.

• 🤙 addScript() - Core function, callback based
• 🙏 loadScript() - Promise based
• 🪝 makeHook() - Create a React/Preact/Mithril/SolidJS hook
• 📀 Install / Use
• 🤨 But why?

addScript()

import { addScript } from "add-javascript";

addScript("https://www.example.com/script.js", options);
// "added" | "already-added" | "already-added (unmanaged)" | "skipped"
//
//    "unmanaged" - means the script was not added by `add-javascript`
//
//    "skipped"   - means `skipLoading()` returned true. Callbacks will
//                  still have run, so this does not imply a no-op.
//

options (defaults shown, see generated index.d.ts for all, loadBehavior visualised here):

// options:
{
  isModule: false,
  loadBehavior: "async",
  fetchPriority: "auto",
  noopIfModulesSupported: false,
  ignoreQueryString: true,
  security: {
    crossOrigin: "",
    nonce: "",
    integrity: "",
    referrerPolicy: "",
    warnOnCrossOrigin: true // warn on absolute cross-origin without integrity
  },
  dataSet: {},
  skipLoading: () => false,
  onLoad: detail => {},
  onError: detail => {}
}

// detail (optional on unmanaged / already-in-DOM paths):
{
  event: Event,
  removeScriptTag: () => void
} | undefined

loadScript()

import { loadScript } from "add-javascript";

loadScript("https://www.example.com/script.js", {
  // Same options as addScript(), but
  // without onLoad and onError since we
  // can use Promise callbacks instead
})
  .then(successDetail => {})
  .catch(failDetail => {});

// Typed as TLoadScriptPromise:
//   .then(successDetail => …)  // TLoadScriptSuccess
//   .catch(failDetail => …)    // TLoadScriptError  (typed on .catch / then's onRejected)

// successDetail (TLoadScriptSuccess — narrow on type):
//   "added" → event + removeScriptTag required
//   "already-added" | "already-added (unmanaged)" → event fields optional
//   "skipped" → skipLoading only (not a cache hit); no event fields

// failDetail (TLoadScriptError):
{
  type: "error",
  event: Event,
  removeScriptTag: () => void
}

// Note: `try { await loadScript(...) } catch (e)` does not type `e` (TypeScript
// limitation). Prefer `.catch`, or narrow: `e as TLoadScriptError`.

// Multiple scripts
await Promise.all([
  loadScript("https://www.example.com/script-1.js", options),
  loadScript("https://www.example.com/script-2.js", options)
]);

// ...or if you have common options:
await Promise.all(
  [
    "https://www.example.com/script-1.js",
    "https://www.example.com/script-2.js"
  ].map(src => loadScript(src, options))
);

makeHook()

React / Preact

import { makeHook } from "add-javascript";
import { useState, useEffect } from "react";

// Make the Hook
const useScriptReact = makeHook({ useState, useEffect });

function ReactComponent(props) {
  // Use it
  const [state, detail] = useScriptReact("./my-script.js", options);
  // state == "pending" | "loading" | "loaded" | "error"
  // detail == undefined until loaded/error, then successDetail | failDetail
  // (typed as TUseScriptReturn — narrow on `state`)

  return <div>{state}</div>;
}

Mithril

import { makeHook } from "add-javascript";
import { withHooks, useState, useEffect } from "mithril-hooks";

// Make the Hook
const useScriptMithril = makeHook({ useState, useEffect });

const MithrilComponent = withHooks(() => {
  // Use it
  const [state, detail] = useScriptMithril("./my-script.js", options);
  // state == "pending" | "loading" | "loaded" | "error"
  // detail == undefined until loaded/error, then successDetail | failDetail

  return m("div", state);
});

SolidJS

import { makeHook } from "add-javascript";
import { createSignal, createEffect } from "solid-js";

// Make the Hook
const useScriptSolidJS = makeHook({
  useState: createSignal,
  useEffect: createEffect
});

function SolidJSComponent() {
  // Use it
  const [state, detail] = useScriptSolidJS("./my-script.js", options);
  // With createSignal as useState, values are often accessors:
  // state() == "pending" | "loading" | "loaded" | "error"
  // detail() == undefined until loaded/error, then success | fail detail

  return html`${state()}`;
}

enabled vs skipLoading

	enabled: false (hook option)	skipLoading: () => true (loader option)
Calls loadScript?	No	Yes
State when “off”	pending, detail undefined	loaded + { type: "skipped" }
Flip off → on	Loads when enabled becomes true	Only if effect re-runs (deps include src / enabled, not arbitrary options)

const [state, detail] = useScript(url, { enabled: isReady });
// enabled defaults to true

React / Preact / mithril-hooks: effect deps are [src, enabled]. Solid’s createEffect ignores the deps array and tracks signals read inside the effect — pass reactive sources accordingly.

You can use all of these frameworks on the same page (if you like.) Check out the tests for a working implementation of this.

Create useScript in its own file for your convenience:

// useScript.js
import { makeHook } from "add-javascript";
import { useState, useEffect } from "react";

export const useScript = makeHook({ useState, useEffect });

// ReactComponent.js
import { useScript } from "./useScript";

function ReactComponent(props) {
  const [state] = useScript("./my-script.js");
  return <div>{state}</div>;
}

Install / Use

$ pnpm i add-javascript

Supports import/require for ESM/CJS.

Browser/UMD version here:

<script src="https://unpkg.com/add-javascript/dist/browser/add-javascript.browser.js"></script>
<script>
  const { loadScript } = addJs;
</script>

But why?

"There are loooads of loadScript/useScript libraries. Why make another one?"

Good question. Perhaps I didn't really need my own library, but I once found myself battling a bug caused by Hot Module Reloading vs. a 3rd-party script and I just ended up writing one to solve the problem. This is the result.

As for the bug, the size of the codebase I was working on at the time make the problem difficult to debug. Long story short, the 3rd-party script was being loaded multiple times and was also not idempotent.

There was also a chance it could be loaded in a vanilla way or via a Hook, hence the desire to offer an API that would consolidate the script-adding logic. This also explains the options default of ignoreQueryString: true, which considers a script loaded regardless of its (in my case: cache-busting) query-string parameters.

The options format is also something of an itch I wanted to scratch.

All that is behind me now, but perhaps someone else will find the outcome of these efforts useful.

Still, if your codebase is under your full control you're likely far better just rolling your own little helper than installing add-javascript:

const loadScript = (src, options = { async: true }) =>
  new Promise((resolve, reject) => {
    const script = document.createElement("script");
    Object.assign(script, options);
    script.onload = resolve;
    script.onerror = reject;
    script.src = src;
    document.body.appendChild(script);
  });

Credits

add-javascript was written by Conan Theobald.

I hope you found it useful! If so, I like coffee ☕️ :)

License

MIT licensed: See LICENSE