opt-args

Simple and unobtrusive JS function overloads for optional arguments

Motivation

There are plenty of npm modules out there that let you do really complex, typed function overloading, but 90% of the time all that's needed is to create convenience methods with less parameters that 'drop' optional arguments.

For example, you might want a function with convenience overloads as follows:

var connect = function(host, port, timeout, handler) { }
 
connect('npmjs.com', 80, 30000, callback);
 
connect('npmjs.com', 80, callback);
 
connect('npmjs.com', callback);
 
connect('npmjs.com');

Implementing the above using the existing modules requires you to define multiple function bodies and add at least half a dozen lines of dead code.

I wanted to achieve this with concise syntax and minimal fuss based purely on the number of arguments passed in.

Approach

First let's deconstruct the overloading in the example above:

• 4 args: connect(host, port, timeout, callback)
• 3 args: connect(host, port, callback)
• 2 args: connect(host, callback)
• 1 args: connect(host)

You can see two clear groups of arguments here - those in italics are "dropped" before those in bold.

This can be represented by assigning a numerical priority to each parameter:

• host: 1
• port: 2
• timeout: 2
• callback: 1

Installation

npm install opt-args

Usage

opt-args allows you to assign a priority to each argument, controlling which arguments To achieve the overloading in the example above with opt-args, define your function as follows:

var opt = require('opt-args');
 
var connect = opt(1,2,2,1, function(host, port, timeout, handler) { });

That's it! Note that only a single funciton body is needed. opt-args ensures that values are routed to the correct parameters.

The four numbers (1,2,2,1) assign a priority to each of the four arguments, with lower values being of higher priority.

Lower priority arguments (higher numerical value) will be "dropped" first, and the right-most of two arguments with the same priority will be dropped first.

Any number of priority groups are supported.

License

ISC