How do I pass command line arguments to a Node.js program?

Question

I have a web server written in Node.js and I would like to launch with a specific folder. I\'m not sure how to access arguments in JavaScript. I\'m running node like this:

Answer 1

Passing arguments is easy, and receiving them is just a matter of reading the process.argv array Node makes accessible from everywhere, basically. But you're sure to want to read them as key/value pairs, so you'll need a piece to script to interpret it.

Joseph Merdrignac posted a beautiful one using reduce, but it relied on a key=value syntax instead of -k value and --key value. I rewrote it much uglier and longer to use that second standard, and I'll post it as an answer because it wouldn't fit as a commentary. But it does get the job done.

   const args = process.argv.slice(2).reduce((acc,arg,cur,arr)=>{
     if(arg.match(/^--/)){
       acc[arg.substring(2)] = true
       acc['_lastkey'] = arg.substring(2)
     } else
     if(arg.match(/^-[^-]/)){
       for(key of arg.substring(1).split('')){
         acc[key] = true
         acc['_lastkey'] = key
       }
     } else
       if(acc['_lastkey']){
         acc[acc['_lastkey']] = arg
         delete acc['_lastkey']
       } else
         acc[arg] = true
     if(cur==arr.length-1)
       delete acc['_lastkey']
     return acc
   },{})

With this code a command node script.js alpha beta -charlie delta --echo foxtrot would give you the following object

args = {
 "alpha":true,
 "beta":true,
 "c":true,
 "h":true,
 "a":true,
 "r":true
 "l":true,
 "i":true,
 "e":"delta",
 "echo":"foxtrot"
}