npm install is not installing grunt js from dependencies - node.js

Question

I am trying to automatic all the package installations automatic for developers. So I have both package.json and grunt file in the same directory. I want to do npm install first so that all dependencies will be installed and when developer executes grunt on command line things will be ready. May I know why it is not working. The other thing is may I know the difference between dependency and devdependencies.
{
"name": "TestProject",
"version": "0.1.0",
"description": "this project is for test",
"main": "index.js",
"dependencies": {
"grunt": "~0.4.2",
"grunt-contrib-uglify": "~0.2.7",
"uglify-js": "~2.4.3",
"grunt-contrib-watch":"~0.5.3",
"grunt-contrib-jshint": "~0.7.2",
"qunit": "~1.11.0"
},
"devDependencies": {
"grunt": "~0.4.2",
"qunit": "~1.11.0",
"grunt-contrib-jshint": "~0.7.2",
"grunt-contrib-nodeunit": "~0.2.0",
"grunt-contrib-uglify": "~0.2.2",
"grunt-contrib-watch": "~0.5.3",
"grunt-contrib-watch":"~0.5.3"
},
"scripts": {
"test": "echo \"Error: no test specified\" && exit 1"
},
"author": "",
"license": "BSD-2-Clause"
}

Answer 1

You are probably missing the command-line utility for Grunt.
That can be installed in your shell, using
npm install -g grunt-cli
The CLI is distributed independently from the grunt package or the grunt- plugins. You should include instructions to install grunt-cli globally in the same dev environment setup documentation where you indicate how to set up node, npm, bower, or the like.
Update
If you are so adamant about installing grunt-cli on npm install, I guess one option might be using npm scripts.
Include in your package.json (note: untested)
{
"postinstall": "npm i -g grunt-cli"
}
I'd discourage this, though. Just install them by hand.