npm install if package.json was modified

Question

TL;DR: Is there a way to have npm install run automatically before running any npm script if your package.json has been modified?

Problem

Answer 1

Okay so I'm done with the package. Here it is. You can use it exactly the same way you specified in your ideal scenario. Just npm install install-changed and add it to a custom script, like pre-run in your example. It should figure out whether or not it needs to npm install and does so if it needs to.

 {
  "scripts": {
    "pre-run": "install-changed",
    "my-script": "…"
  },

You can also do this programatically but I don't think you're going to need this.

let installChanged = require('install-changed')

let isModified = installChanged.watchPackage() 

The function above does exactly the same thing, additonally it also returns a boolean value which you might find useful.

Answer 2

Like other answers, but I think simpler because it's one line of shell script in package.json:

{
    "scripts": {
        "install-if-needed": "[ package.json -nt node_modules ] && npm install && touch node_modules",
        "my-script": "npm run install-if-needed && ..."
    }
}

or, basically equivalent:

{
    "scripts": {
        "install-if-needed": "[ package.json -nt node_modules ] && npm install && touch node_modules",
        "premy-script": "npm run install-if-needed",
        "my-script": "..."
    }
}

You'll have to either inline npm run install-if-needed or have a pre... script for each script that needs it -- I don't know any other way to have it run before multiple other scripts.

Explanation: install-if-needed checks the modification times on package.json and node_modules. If node_modules is newer, it does nothing; otherwise it runs npm install. The final touch node_modules is necessary because npm install may itself change the package.json modification time (if it is correcting whitespace in package.json for example).

Answer 3

You can create a custom script that will run your smart install.

smart-install.sh file

#!/usr/bin/env bash

changedFiles="$(git diff-tree -r --name-only --no-commit-id ORIG_HEAD HEAD)"

checkForChangedFiles() {
    echo "$changedFiles" | grep --quiet "$1" && eval "$2"
}

packageJsonHasChanged() {
  echo "Changes to package.json detected, installing updates"
  npm i
}

checkForChangedFiles package.json packageJsonHasChanged

Then if you have husky you can add that to the post-checkout hook or any hook you like. If you don't have husky, you can also add it directly to the scripts which essentially do the same thing.

.huskyrc file

{
  "hooks": {
    "post-checkout": "npm run smart-install"
  }
}

package.json file

"scripts": {
  ...
  "smart-install": "bash ./bin/smart-install.sh",
}

Either way it's a good idea to create a npm script to run smart-install