Parse function arguments. Useful to implement variadic functions.
Last updated a year ago by okunishinishi .
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Parse function arguments. Useful to implement variadic functions.


npm install argx --save


Pass the arguments object to .argx() inside your function.

 * This is an example to declare an variadic functions.
'use strict'

const argx = require('argx')

function doSomething (values, options, callback) {
  let args = argx(arguments)
  callback = args.pop('function') || function noop () {} // Consume last argument if it's a function.
  options = args.pop('object') || {} // Consume last argument if it's an object.
  values = args.remain() // Get remaining arguments as array.
  /* ... */

doSomething('foo', 'bar')
doSomething('foo', 'bar', { verbose: true })
doSomething('foo', 'bar', (err) => {})
doSomething('foo', 'bar', { verbose: true }, (err) => {})

API Guide

API guide for Argx instance, which is returned by argx(arguments).

Signature Description Example
.pop() Pop an argument value from last. args.pop()
.pop(count) Pop multiple values from last. Orders are preserved. args.pop(1)
.pop(type) Pop only if the last value conform the type. args.pop("number")
.pop(count, type) Pop values while conforming the type. args.pop(2, "number")
args.pop(1, CustomObj)
.shift() Shift an argument value from top. args.shift()
.shift(count) Shift multiple values from top. args.shift(2)
.shift(type) Shift only if the top value conform the type. args.shift("string")
.shift(count, type) Shift values while conforming the type. args.shift(2, "string")
args.shift(4, CustomObj)
.remain() Shift all remained values. Always returns an array. args.remain()


Detecting Custom Types.

Type which .pop()/.shift() accept is string, a custom object or a custom constructor.

function MyConstructor(){/*...*/};
args.pop(MyConstructor); // Pop only if the last argument is instantiate by `new MyConstructor()`

var MyObj = {/*...*/};
args.pop(MyObj); // Pop only if the last argument is create by `Object.create(MyObj)`

Specify Multiple Types

There are two ways to specify 'or' condition for types.

  1. Passing string joined by "|" (eg: args.pop('string|number'); )
  2. Passing array as type (eg: args.pop(['string', MyCustomObj]); )

Want Array Always

Note that .pop()/.shift() methods returns values as array only when multiple entries hit. If you want to make sure to keep values as array, use [].concat().

var args = argx(arguments);
var values = [].concat(args.pop(2, 'string') || []); // Always array.


This software is released under the MIT License.

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