Uncaught referenceerror process is not defined

Video Uncaught referenceerror process is not defined

Common Error

This error is common in many frontend projects. You might have encountered it a few times, and it might come from a line of code like this:

// This causes the error const { NODE_ENV } = process.env;

And the solution is:

// This fixes the problem const NODE_ENV = process.env.NODE_ENV;

Why the Error?

Force the error now. Open the console and type the following:

> console.log(process); Uncaught ReferenceError: process is not defined

Now, try the same in NodeJS. Create a file or open the node repl and run console.log(process):

> console.log(process); process { version: ‘v14.18.1’, versions: { node: ‘14.18.1’, //…

In NodeJS, “process” is defined, but not in the browser. This is because NodeJS and the browser are different runtime environments.

Build Step

Most frontend projects have a build step; this build step is executed in NodeJS.

The build step is in charge of removing the process dependency so that it doesn’t get to the browser. It changes the values to something like the following:

const NODE_ENV = ‘development’;

These values depend on the environment variables when executing the build.

Try It with Webpack

Read more: Steve s card computer

I built a Webpack toy project, where I have the following code:

console.log(‘hello world’); const { NODE_ENV } = process.env; console.log(NODE_ENV);

When I run the build step, Webpack creates the following file that will be then sent to the browser.

(() => { console.log(“hello world”); const { NODE_ENV: o } = process.env; console.log(o); })();

The reference to process has not disappeared after the build step. It’s still there, and therefore, the browser complains that it doesn’t understand process.

Try the Fix

What happens when I change my code to:

console.log(‘hello world’); const NODE_ENV = process.env.NODE_ENV; console.log(NODE_ENV);

Then the build step outputs the following:

console.log(“hello world”),console.log(“production”);

Now, the process reference has disappeared and been replaced by the value of the environment variable at build time.

Why the Fix?

Why does the fix work?

const NODE_ENV = process.env.NODE_ENV;

By default, the build step does a simple replacement of strings. So, for example, in the Webpack configuration, I have the following:

plugins: [ new webpack.DefinePlugin({ ‘process.env.NODE_ENV’: JSON.stringify(env.NODE_ENV), }), ],

Read more: Totallyscience co games

With the previous configuration, Webpack replaces the text process.env.NODE_ENV for the value during the build process.

If you like this article, join more than 2,000 subscribers.

Every other Wednesday, I share an article on a topic that you don’t learn at work.

Thanks for subscribing! A confirmation email has been sent.

Check the SPAM folder if you don’t receive it shortly.

Sorry, there was an error ?.

Try again and contact me at llorenc[at]gimtec.io if it doesn’t work. Thanks!


Why Doesn’t Deconstruction Work?

Aren’t both codes the same?

const { NODE_ENV } = process.env; // isn’t this the same? const NODE_ENV = process.env.NODE_ENV;

Read more: Failed building wheel for h5py

For the language, they are the same. Yet, the build process takes a straightforward approach: it replaces text.

In the first example:

const { NODE_ENV } = process.env;

The text process.env.NODE_ENV is nowhere to be found. Therefore, the build step can’t replace it.

Understand the Steps and Runtime Environment

Keep in mind: “Where is the line of code executed?”. There are several answers: in the client, during the build, during a test, or any other step you might have. This helps you understand the runtime environment and therefore catch possible errors faster.

In this case, process is not defined in the browser environment, hence the error. The solution is to remove the reference to process, and replace it with the value you need during the build step.

If you like this post, consider sharing it with your friends on twitter or forwarding this email to them ?

Don’t hesitate to reach out to me if you have any questions or see an error. I highly appreciate it.

And thanks to Bernat, Michal and Miquel for reviewing this article ?

Related Posts