By default, commandLineArgs will throw an exception if the user set an unexpected option or value. This is often what we need, although there are times when need to be permissive, for example when collecting args we intend to pass to a different application. To achieve this we use partial parsing mode.

In this example, we define a --value option and enable partial parsing (set partial: true in the commandLineArgs options). Save the script as example.js.

const commandLineArgs = require('command-line-args')
const optionDefinitions = [
  { name: 'value', type: Number }
]
const options = commandLineArgs(optionDefinitions, { partial: true })
console.log(options)

Set one known option (--value) and two unknown options (--milk and --bread).

$ node example.js --milk --value 2 --bread cheese

Notice the _unknown property contains the unknown args. No exceptions are thrown.

{
  value: 2,
  _unknown: [ '--milk', '--bread', 'cheese']
}