npm run dev

Problem : laravel-5-4-cross-env-is-not-recognized-as-an-internal-or-external-command

You need to make cross-env working global instead of having in in the project.

1) remove node_modules folder

2) run

npm install --global cross-env

3) remove "cross-env": "^5.0.1", from package.json file devDependencies section. Actually, you can skip this step and keep package.json intact. If you prefer.

4) run

npm install --no-bin-links

5) run

npm run dev

and see it working