Using third-party libraries is very common while developing apps for the web. The usual way is to install the NPM package of the library and import it for your use.

But sometimes, the NPM package is unavailable, or you have to include files directly from a CDN or external source. Adding <script> tags in the index.html file does not work every time, and even if it does, it could cause issues as the website scales.

I faced a similar issue while adding Calendly import to my portfolio site and found an easy solution. But first, let's understand why exactly an error occurs when you add <script> tags in React components.

Why it Throws an Error

React uses React DOM to render JSX content on the web page. React DOM is a virtual DOM that resides on top of the original DOM. It only updates changed nodes from the DOM, unlike the original DOM, which completely updates itself after every change. React DOM uses createElement to convert JSX into DOM elements.

The createElement function uses the innerHTML API to add changed nodes in the browser's original DOM. HTML5 specifications state that <script> tags are not executed if they are inserted with innerHTML. MDN Web Docs have explained the security reasons behind this.

As a result, the execution of the <script> tag throws an error in React.

The Solution

The simplest solution is to add scripts directly into DOM using the Document interface provided by web APIs. We can use JavaScript's DOM manipulation methods to inject the <script> tag without React DOM interfering.

Here is what we have to do:

At first, we get head and script tags from DOM.
Then, we use the setAttribute method to add a new script.
The modified script tag is appended to the head.

In React terms, the desired script has to be added to DOM when the component loads on the browser. React has a hook for such scenarios: useEffect. The whole process explained above can be wrapped inside the hook and triggered when the component renders for the first time or a new script is added.

In real-world projects, we might want to add multiple scripts. Hence, it's better to create a custom hook, so we can call it multiple times with different source links.

Custom hooks are usually stored in a separate directory within the /src folder. Let's create a new file inside the /src/hooks/ directory and name it useExternalScripts.js. Paste the following code in the file:

import { useEffect } from 'react';

export default function useExternalScripts({ url }){
  useEffect(() => {
    const head = document.querySelector("head");
    const script = document.createElement("script");

    script.setAttribute("src", url);
    head.appendChild(script);

    return () => {
      head.removeChild(script);
    };
  }, [url]);
};

In a component where you want to add a new script, paste the following code:

import useExternalScripts from "./hooks/useExternalScripts"

const Component = () => {
  useExternalScripts("https://www.scriptdomain.com/script")
  ...
}

A new script is appended to the head of the page whenever the component is mounted in the DOM. The script is removed when the component unmounts.

Don't use the return snippet if your script is used in multiple components throughout your app. The function returned by the hook is a cleanup function, which is executed when a component is unmounted. Hence, we don't require it if we have to use the source at multiple places.

Alternate Solution

Alternatively, you can use react-helmet, which manages changes within the <head> tag. The <Helmet> can take care of the script if it is placed inside of it.

import { Helmet } from "react-helmet"

export default function Component() {
  return (
    <>
      <Helmet>
        <script
          src="https://www.myscripts.com/scripts"
          crossorigin="anonymous"
          async
        ></script>
      </Helmet>
      ...
    </>
  )
}

Don't forget to install react-helmet before you start your app!

Wrapping Up

React uses innerHTML at the core to manipulate nodes on the browser's DOM. The innerHTML API doesn't support <script> tags for security reasons. Hence, an error is thrown if you try to inject a <script> tag in a React component.

Adding a new script tag and directly appending it to the <head> element of the page is the easiest way to add <script> tags in the React app. react-helmet is a third-party library that can be used to achieve the same thing by handling the <head> tag on every page.

I feel the custom hook version is better than using a third-party library since we have full control over it. What do you think? Did you use any other method? Let me know down below!

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Until then, happy debugging! ⛑

Also published here

How to Add Script Tags in React