How to Make an External JavaScript File Work in ReactJS

Learn how to successfully integrate and utilize `external JavaScript files` within your ReactJS application for enhanced functionality and user experience.
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This video is based on the question https://stackoverflow.com/q/66827621/ asked by the user 'John Wink' ( https://stackoverflow.com/u/7763754/ ) and on the answer https://stackoverflow.com/a/66827646/ provided by the user 'mesibo' ( https://stackoverflow.com/u/4895359/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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How to Make an External JavaScript File Work in ReactJS

Integrating external JavaScript files in a ReactJS application can be a challenge for many developers, especially if you're used to managing your scripts in a traditional HTML environment. In this guide, we'll explore a common problem where external scripts fail to work, and we'll provide a step-by-step solution to ensure they function seamlessly alongside your React components.

The Problem

In a typical React project, the main entry point is usually a public.html file where we integrate various assets. For instance, you might have an external JavaScript file from a theme that you want to use in one of your components. However, when you try to use properties from this external JavaScript file, it doesn't work as expected.

Example Scenario

Consider the following simplified setup in your public.html file:

[[See Video to Reveal this Text or Code Snippet]]

You've included function.js, which contains vital functions or properties from a theme. However, when you attempt to access an HTML element like an input field within this external file, it returns null, indicating that the script isn’t correctly loaded or executed in relation to the React component lifecycle.

In the Component

As an example, you might have the following input field in your React component:

[[See Video to Reveal this Text or Code Snippet]]

When you use console.log(document.getElementById("userName")) inside componentDidMount(), it outputs the input element correctly. But trying the same in function.js gives you null. So, how do you make this external JavaScript file work effectively within your React application?

Solution: Loading External JavaScript in ReactJS

To properly integrate external JavaScript files in React, you need to load them using the DOM methods provided by JavaScript. This way, you ensure that the script is added after the component has been rendered to the DOM.

Step-by-Step Guide

Create a Script Element:
Use document.createElement("script") to create a script element.

[[See Video to Reveal this Text or Code Snippet]]

Append the Script to the Body:
Add the script element to the body of your HTML document.

[[See Video to Reveal this Text or Code Snippet]]

Integrate into Your Component:
Insert this script-loading logic in a lifecycle method such as componentDidMount() of your React component.

[[See Video to Reveal this Text or Code Snippet]]

Why This Works

By appending the external script in the componentDidMount() method, you ensure that the DOM is fully rendered before the script executes. This means when the external script runs, it can access and manipulate any elements present in the DOM, such as the <input> field with the ID userName.

Conclusion

Integrating external JavaScript files into your ReactJS app doesn't have to be a headache. As demonstrated, leveraging the DOM API to create and append script elements will allow you to successfully use the external functionalities you need. This method not only enhances the capabilities of your application but also maintains the responsiveness that comes with using React.

By following these steps, you can effectively enhance your React components with the power of external libraries, ensuring they work in harmony with your existing codebase.

If you have questions or need further assistance with ReactJS or external libraries, feel free to reach out in the comments below!

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