[NPM] Pass arguments to npm scripts

Often times you’ll have variations that you’ll want to make to your npm scripts and repeating yourself is inefficient and verbose. Instead you can create a base script and pass arguments into it from another script.

For example, you have a script:

"test": "mocha spec/ --require babel-register",

And you want to add a watcher to the test script:

"test:watch": "mocha spec/ --require babel-register --watch",

Here what we do is copy the script and add a '--watch' behind. This is not good enough, because if you want to change the 'test' script, you also need to modify the 'test:watch' script.

So what you can do:

"test:watch": "npm t -- --watch"

First '--' tell the compiler that we still need to pass in some arguments; And '--watch' is what we want to pass in.