is-npm 
Check if your code is running as an npm or yarn script
Install
$ npm install is-npm
Usage
const {isNpmOrYarn, isNpm, isYarn} = require('is-npm');
console.table({isNpmOrYarn, isNpm, isYarn});
$ node foo.js
# ┌─────────────┬────────┐
# │ (index) │ Values │
# ├─────────────┼────────┤
# │ isNpmOrYarn │ false │
# │ isNpm │ false │
# │ isYarn │ false │
# └─────────────┴────────┘
$ npm run foo
# ┌─────────────┬────────┐
# │ (index) │ Values │
# ├─────────────┼────────┤
# │ isNpmOrYarn │ true │
# │ isNpm │ true │
# │ isYarn │ false │
# └─────────────┴────────┘
$ yarn run foo
# ┌─────────────┬────────┐
# │ (index) │ Values │
# ├─────────────┼────────┤
# │ isNpmOrYarn │ true │
# │ isNpm │ false │
# │ isYarn │ true │
# └─────────────┴────────┘
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