Why does `DEBUG=foo node index.js` fails in `scripts` section of `package.json`

I'm on Windows 10, but I'm using git bash. When running from git bash the following:

DEBUG=foo node index.js

it works fine and sets the environment variable DEBUG. But if I put it into the scripts section of the package.json:

  "scripts": {
    "start": "DEBUG=foo node index.js"
  },

and run the following from git bash I get the following error:

$ npm start

> nodejs@1.0.0 start C:\Users\maksym.koretskyi\Desktop\nodejs
> DEBUG=foo node index.js

'DEBUG' is not recognized as an internal or external command,
operable program or batch file.

Why the behaviour?

rsp

It seems like you're running it on Windows.

Assuming that you have Bash working as you said, I would make a script:

#!/bin/bash
DEBUG=foo node index.js

called e.g. run-debug and use:

"scripts": {
    "start": "bash run-debug"
},

in package.json to make sure that the DEBUG=foo node index.js command is interpreted by Bash and not command.com or whatever the shell in Windows is called. See Issue #6543: npm scripts shell select.

For cases when you want it to run even on systems without Bash, for maximum cross-platform compatibility, it's even better to use a Node script instead of a shell script:

"scripts": {
    "start": "node run-debug.js"
},

In this case the run-debug.js could contain something like:

let env = Object.create(process.env);
env.DEBUG = 'foo';
spawn('node', ['app.js'], {env});