The "npm err! missing script: dev" error is a common problem faced by developers working with Node.js and npm. This error occurs when you try to run a script that does not exist in your package.json file. In this guide, we will explain what causes this error and provide a step-by-step solution to fix it.
Table of Contents
What causes the "npm err! missing script: dev" error?
When you run npm run dev or a similar command, npm looks for a script named dev in your package.json file. If it cannot find a script with that name, it throws the "npm err! missing script: dev" error.
This error typically occurs when:
- The
devscript is not defined in thepackage.jsonfile. - The script name is misspelled or has a typo.
- The
package.jsonfile is not located in the root directory of the project.
Step-by-step guide to fix the error
Step 1: Check your package.json file
Open your package.json file and look for the scripts section. Ensure that there is a dev script defined. If it's missing, add a dev script that executes your desired development command, such as starting your development server or running your app in development mode.
For example, if you are using Express.js, your scripts section should look like this:
"scripts": {
"start": "node app.js",
"dev": "nodemon app.js"
}
Step 2: Verify the script name
If the dev script is defined in your package.json file, make sure it is spelled correctly and does not have any typos.
Step 3: Check the location of the package.json file
Ensure that the package.json file is located in the root directory of your project. If it is in a subdirectory, move it to the root directory or change your terminal's working directory to the directory containing the package.json file.
Step 4: Reinstall npm packages
If you have made any changes to your package.json file or moved it to a different location, you may need to reinstall your npm packages. Run the following command in your terminal:
npm install
Step 5: Run the dev script
After addressing the issues in the previous steps, try running the dev script again:
npm run dev
If you have followed these steps, the "npm err! missing script: dev" error should be resolved.
FAQs
1. What is the dev script used for?
The dev script is commonly used to run your application in development mode, which may include features like hot-reloading, debugging, or running in a local environment.
2. How do I create custom npm scripts?
To create custom npm scripts, add a new key-value pair in the scripts section of your package.json file. The key will be the script name, and the value will be the command to execute. For example:
"scripts": {
"start": "node app.js",
"custom-script": "node custom-script.js"
}
3. Can I use environment variables in npm scripts?
Yes, you can use environment variables in npm scripts by referencing them with process.env.YOUR_VARIABLE_NAME. For example:
"scripts": {
"start": "node app.js",
"dev": "NODE_ENV=development nodemon app.js"
}
4. How do I run multiple npm scripts in parallel?
To run multiple npm scripts in parallel, you can use the npm-run-all package or similar tools. Install the package with the following command:
npm install npm-run-all --save-dev
Then, you can create a new script in your package.json file that runs multiple scripts in parallel:
"scripts": {
"start": "node app.js",
"dev": "nodemon app.js",
"build": "webpack",
"start:dev": "run-p dev build"
}
5. How do I check the list of all available npm scripts?
To view the list of all available npm scripts in your project, run the following command in your terminal:
npm run
This will display a list of all the scripts defined in your package.json file.
Related Links
Conclusion
In this guide, we've covered the common causes of the "npm err! missing script: dev" error and provided a step-by-step solution to fix it. Be sure to double-check your package.json file to ensure your scripts are correctly defined and located in the right directory.