Fixing the Unexpected token = Error in Jest When Testing JavaScript Enums

Summary: Learn how to address the "SyntaxError: Unexpected token =" error in Jest when testing JavaScript enums with this detailed guide.
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Fixing the Unexpected token = Error in Jest When Testing JavaScript Enums

If you've been working with JavaScript enums and running tests with Jest, you might have come across this pesky error: SyntaxError: Unexpected token =. This can be frustrating, but understanding why it happens is the first step towards resolving it. Let's break down the problem and offer a solution.

Understanding the Error

The error message typically looks something like this:

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This error occurs because Jest's environment settings might not be configured to understand some of the newer JavaScript syntax. Enums in JavaScript often make use of syntax that isn't natively supported by Jest without certain configurations.

Why Does This Happen?

Jest, by default, uses Babel to transpile JavaScript code. However, if your enum code uses syntax that Babel doesn't transpile out-of-the-box, you will see the Unexpected token error. This can particularly be the case when using class properties or other modern JavaScript features.

For example, the following enum might cause an issue:

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

Here, the static properties use the = syntax which Jest might not handle correctly due to missing Babel plugins.

Solution

Step 1: Install the Required Babel Plugin

To fix this, you need to ensure that Babel is set up to handle modern syntax. Install @babel/plugin-proposal-class-properties to manage class properties syntax:

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Step 2: Update Your Babel Configuration

.babelrc

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Step 3: Validate and Test

With the Babel configuration updated, Jest should now be able to parse the modern JavaScript syntax used in your enums.

Run your tests again:

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

You should no longer see the SyntaxError: Unexpected token = message, and your tests should run successfully.

Conclusion

Jest throwing a SyntaxError: Unexpected token = error when testing JavaScript enums boils down to a configuration issue. By ensuring that Babel is correctly set up to transpile modern JavaScript syntax, you can overcome this issue. Install the @babel/plugin-proposal-class-properties plugin and update your Babel configuration to resolve this error, allowing your tests to run smoothly.

Happy testing with Jest!