In many React projects, there often comes a time when you'll want to integrate with a third party service that uses their javascript. Maybe it's an analytics or tracking service, or a data or graphics provider like Google Maps. Whatever it is, injecting the external script can be tricky at the component level. It's easy if you want to just put it in the header or footer for everything, but that can lead to poor performance and a poor user experience. Let's use those fancy React Hooks for something useful.

import { useEffect } from 'react';

function ScriptInjector() {

    /* Let's imagine we need to append our key to the url for 
    example, there's often some identification that needs to 
    be supplied */
    const ourApiKey = '123456789`;
    const thirdParyUrl = 'https://theirscript.js';

    // We'll use useEffect to load once when component is mounted
    useEffect(() => {
        // Obviously, id has to match what's used in id below
		const existingScript = document.getElementById('third-party-script');

        // Ensure it's only loaded on the page once
		if (!existingScript) {
			const thirdPartyScript = document.createElement('script');
			thirdPartyScript.src = thirdParyUrl + '?key=' + ourApiKey;
			thirdPartyScript.id = 'third-party-script';
			document.body.appendChild(thirdPartyScript);

            /* In some instances, we need to initiate their script 
            from our side once the external script has loaded, in 
            that case, I create my own js file that calls their 
            function, and load it on the page, after the external 
            script has loaded */
			thirdPartyScript.onload = () => {
				const initFunction = document.createElement('script');
				initFunction.src = '/static/initFunction.js';
				initFunction.id = 'initFunction';
				document.body.appendChild(initFunction);
			};
		}
	});

	return null;
}

export default ScriptInjector;

Since I removed parts specific to my business use to make this more generic, I haven't tested this code as is. I apologize if I missed something, but I hope this gets the idea across. Many of the variables are only used once and I left them in for readability, but you could drop them in favor of more concise code as well.

When you go to use this component on the page or within another component, you'll import this one, then place it in the render method as you would with any other component.

import ScriptInjector from 'components/ScriptInjector';

// Then inside render method

<ScriptInjector />

Another thing that could be done is to pass the script url in as a prop, however, many outside services format their urls and api key requirements differently, so ensuring the format works for multiple services may get complicated.