Скачать или смотреть How to Optionally Use the window Variable in Node/Browser Modules

A guide on how to prevent errors related to the `window` variable when using UMD modules in NodeJS. Learn the correct way to check for the existence of `window` to ensure your scripts run smoothly.
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This video is based on the question https://stackoverflow.com/q/67913946/ asked by the user 'Josh M.' ( https://stackoverflow.com/u/374198/ ) and on the answer https://stackoverflow.com/a/67914276/ provided by the user 'jfriend00' ( https://stackoverflow.com/u/816620/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Understanding the Problem: window Variable in NodeJS

If you’ve been working with JavaScript in both a browser and NodeJS environment, you may have encountered a situation where your Node.js script fails because it tries to use the window variable. This can be particularly puzzling if you're using a library that is meant to work in both environments, but references window without proper checks.

The Scenario

You might run into an error like this when using a UMD module in Node:

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

This error occurs due to the attempt to access window, which does not exist in Node.js since it operates in a non-browser environment.

The Culprit

The line of code in question often looks like this:

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

At first glance, it seems like a correct check to see if window is defined. However, as it stands, this check will not work as intended.

The Solution: Correcting the Type Check

To resolve this issue, you need to ensure that you are actually checking the type as a string. Specifically, the comparison must be against the string "undefined" rather than the identifier undefined. Here’s how to properly modify the code.

The Correct Code

Change your code to the following:

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

This small adjustment ensures that the comparison correctly checks the type of window.

Breakdown of the Fix

Use of typeof: This operator can safely check if a variable or global object is accessible without causing a ReferenceError if it's not defined.

String Comparison: Change undefined to "undefined" so that you check the string result of typeof.

Fallback Handling: The code provides a fallback to an empty string if window is not available, making it safe to run in NodeJS.

Conclusion: A Handy Tip for Node and UMD Modules

When dealing with libraries or code that might reference the window variable, always ensure that you perform the correct type checks to prevent runtime errors. The mistake of comparing with the singular undefined instead of the string "undefined" can lead to frustrating debugging sessions.

By following the solution provided here, you can ensure that your Node.js scripts that utilize UMD modules run smoothly without encountering the window is not defined error.

Now, you're equipped with the knowledge and the fix to effectively handle the window variable across Node and browser environments. Happy coding!