How to disable warnings when node is launched via a (global) shell script

Question

I am building a CLI tool with node, and want to use the fs.promise API. However, when the app is launched, there's always an ExperimentalWarning, which is super annoying and messes up with the interaction prompts. How can I disable this warning/all warnings?

I'm testing this with the latest node v10 lts release on Windows 10.

To use the CLI tool globally, I have added this to my package.json file:

    { 
      //...
      "preferGlobal": true,
      "bin": { "myapp" : "./index.js" }
      //...
    }

And have run npm link to link the ./index.js script. Then I am able to run the app globally simply with myapp.

After some research I noticed that there are generally 2 ways to disable the warnings:

set environmental variable NODE_NO_WARNINGS=1
call the script with node --no-warnings ./index.js

Although I was able to disable the warnings with the 2 methods above, there seems to be no way to do that while directly running myapp command.

The shebang I placed in the entrance script ./index.js is:

#!/usr/bin/env node


// my code...

I have also read other discussions on modifying the shebang, but haven't found a universal/cross-platform way to do this - to either pass argument to node itself, or set the env variable.

If I publish this npm package, it would be great if there's a way to make sure the warnings of this single package are disabled in advance, instead of having each individual user tweak their environment themselves. Is there any hidden npm package.json configs that allow this?

Any help would be greatly appreciated!

score 22 · Accepted Answer · answered May 12 '19 at 03:14

I am now using a launcher script to spawn a child_process to work around this limitation. Ugly, but it works with npm link, global installs and whatnot.

#!/usr/bin/env node
const { spawnSync } = require("child_process");
const { resolve } = require("path");

// Say our original entrance script is `app.js`
const cmd = "node --no-warnings " + resolve(__dirname, "app.js");
spawnSync(cmd, { stdio: "inherit", shell: true });

As it's kind of like a hack, I won't be using this method next time, and will instead be wrapping the original APIs in a promise manually, sticking to util.promisify, or using the blocking/sync version of the APIs.

Gilbert · Answer 2 · 2023-07-14T07:59:28.140

I configured my test script like this:

 "scripts": {
    "test": "tsc && cross-env NODE_OPTIONS=--experimental-vm-modules NODE_NO_WARNINGS=1 jest"
  },

Notice the NODE_NO_WARNINGS=1 part. It disables the warnings I was getting from setting NODE_OPTIONS=--experimental-vm-modules

Update

It should also be noted that you dont need to target the typescript code in your tests. Infact, you can write your tests in JavaScript using commonjs and target the dist folder that has the output of your build.

score 9 · Answer 3 · answered Aug 29 '22 at 08:12

New answer: You can also catch emitted warnings in your script and choose which ones to prevent from being logged

const originalEmit = process.emit;
process.emit = function (name, data, ...args) {
  if (
    name === `warning` &&
    typeof data === `object` &&
    data.name === `ExperimentalWarning` 
    //if you want to only stop certain messages, test for the message here:
    //&& data.message.includes(`Fetch API`)
  ) {
    return false;
  }
  return originalEmit.apply(process, arguments);
};

Inspired by this patch to yarn

score 6 · Answer 4 · answered Aug 12 '20 at 16:32

Here's what I'm using to run node with a command line flag:

#!/bin/sh
_=0// "exec" "/usr/bin/env" "node" "--experimental-repl-await" "$0" "$@"

// Your normal Javascript here

The first line tells the shell to use /bin/sh to run the script. The second line is a bit magical. To the shell it's a variable assignment _=0// followed by "exec" ....

Node sees it as a variable assignment followed by a comment - so it's almost a nop apart from the side effect of assigning 0 to _.

The result is that when the shell reaches line 2 it will exec node (via env) with any command line options you need.

score 4 · Answer 5 · answered Feb 22 '23 at 17:54

I needed to suppress:

ExperimentalWarning: Importing JSON modules is an experimental feature and might change at any time

And this worked for me on Windows, Node.js 18.x:

#!/usr/bin/env node --no-warnings

After install --no-warnings added to node calls inside bin scripts .cmd, .ps

I guess this won't work for Linux. I didn't manage to find universal solution

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How to disable warnings when node is launched via a (global) shell script

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