ArgueJS is a JavaScript library that allows you to delightfully extend your method's signatures with optional parameters, default values and type-checking.

example

Let's suppose we want to rewrite the well known method range from underscorejs.

Note that documentation says its method signature is range([start], stop, [step]). With ArgueJS we could type just this way:

function range(){ 
  arguments = __({start: [Number, 0], stop: Number, step: [Number, 1]})

  for(var i = arguments.start; i < arguments.stop; i += arguments.step)
    console.log(i);
}

>>> range(3)
 0
 1
 2
>>> range(3, 5)
 3
 4
>>> range(0, 5, 2)
 0
 2
 4

Installation

ArgueJS is available for both node.js and the browser.

Node.js

Package is available through npm:

$ npm install arguejs

Browser

Include the ArgueJS browser build in your pages.

<script src="argue.js" type="text/javascript"></script>

This will provide __ as a global object, or define it if you are using AMD.

The latest version will be available for hot-linking at http://raw.github.com/zvictor/ArgueJS/master/argue.js. If you prefer to host yourself, use the argue.js file from the root of the github project.

Getting started

When writing your JavaScript methods with ArgueJS, have in mind that you will not use conventional parameters definition as you used before. Actually, all your methods should be defined without them.

Just at the beginning of your method scope, you should pass an object defining your method signature into a call to __ and save its reference for later. The signature of this method is Object __(Object signature, [Object upperArguments])

example:

function person(){
  var signature = {name: String, age: Number};
  arguments = __(signature);
  // String name is now referenced by arguments.name
  // Number age is now referenced by arguments.age
  return arguments;
}

>>> person('John', 27).name
 'John'
>>> person('John', 27).age
 27

Propagating arguments

It is recommended that you explicitly pass your methods arguments through ArgueJS. It is not required, unless if running in strict mode or aiming compatibility of your code with future versions of JavaScript, then it is required.

To explicitly pass your methods arguments through ArgueJS, just pass the arguments variable after the signature description object, like this example does:

function person(){
  args = __({name: String, age: Number}, arguments);
  // ...

See how does the arguments inference works for more.

Type-checking

Type-checking ensures your arguments are what you expected, and throws errors when not.

example:

function age(){
  arguments = __({born: Date})
  // ...

>>> age('01/10/1988')
 Error: parameter 'born' waiting for a Date argument but received a String

Avoid type-checking

The primitive data type null can be used to allow the argument to be of any type.

example:

function book(){
  arguments = __({title: null})
  // ...
  return arguments.title;
}

>>> book('Animal Farm: a Fairy Story')
 'Animal Farm: a Fairy Story'
>>> book(1984)
 1984

The relation of ArgueJS with undefined and null values is detail explained at our Wiki page Null and Undefined types

Data types

• String
• Number
• Boolean
• Array
• Function
• Object
• Date
• RegExp

Special data types:

• "global" (or __.type.global)
• "Arguments" (or __.type.Arguments)

Optional parameters

Optional parameters are great to avoid a mess of conditional clauses at the beginning of your method. To make a parameter optional, declare its type inside of an Array, like this: {name: [String]}

example:

function unique(){
  arguments = __({array: Array, isSorted: [Boolean], iterator: [Function]})
  // Array array is required
  // Boolean isSorted is optional
  // Function iterator is optional
  
  // ...

If no value is passed to an optional parameter, then its argument value will be undefined. To set a default value for your parameter, take a look at default values.

Default values

When writing methods, sometimes you want to override the value of an undefined argument by a default value. The syntax to do this is similar to optional parameters. That is because a parameter with default value is an optional parameter by definition.

To set a default value for a parameter declare its type and its default value inside of an Array, like this: {name: [String, 'unknown']}

example:

function unique(){
  arguments = __({array: Array, isSorted: [Boolean, false], iterator: [Function, function(element){
    return element;
  }]})
  // Array array is required
  // Boolean isSorted is optional and its default value is false
  // Function iterator is optional and its default value is the function declared above
  
  // ...

If you do not care about its type, but just want it to have a default value, you should type your parameter as undefined

example:

  arguments = __({name: [undefined, 'unknown']});

Utilities

Some JavaScript methods do not work intuitively when dealing with types. This is why we made available these utilities methods, to help you to better deal with them.

typeof

Method that gives us the String representation of the type of a given object.

Consider the following example, using the native typeof method:

> function whichType() {
  return typeof this;
}
> [
  whichType.call(false),    // "boolean", right? No!
  whichType.call("hello"),  // "string", right?  No!
  whichType.call(123),      // "number", right?  No!
];
[ 'object', 'object', 'object' ]

Replace the function whichType to use ArgueJS' __.typeof and you will have the expected values:

function whichType() {
  return __.typeof( this );
}

[ 'Boolean', 'String', 'Number' ]

getType

The method __.getType gives us the type class of the object we may want to inspect. Why using String representations when we can access the type directly?

> __.getType({key:"value"}) === Object
true
> constructor = __.getType(7)
[Function: Number]
> constructor("myString") // Number("myString")
NaN
> __.getType(this)
[Function: global]

belongs

The method __.belongs tells us if a given instance belongs to the given type class. No excuses to compare String representations anymore!

> __.belongs({key:"value"}, Object)
true
> __.belongs(this, __.type.global)
true
> __.belongs("value", Number)
false

noConflict

Utility to recover the ownership over the __ variable.

var ArgueJS = __.noConflict();
// Now, __ makes reference to its old value, the one before you added ArgueJS

FAQ

How does the arguments inference works?

To automatically infer your method arguments, ArgueJS uses arguments.callee internally. It is a powerful and old resource but won't be supported in future JavaScript versions anymore, and this is why strict mode disallows its use.

Nowadays it is present in all major browsers, although its use is not recommended in favor of better performance. See its documentation for even more.

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Contributing

This project is on its very early stages and any help, suggestion or posted issue will be very appreciated.