Opex NPM | npm.io

opex

opex (Options Extender) is a tiny, fast extend/mixin function with n-args and functions-as-objects support.

var opex = require('opex'),
  defaults = {
    // your defaults
  };

function example(options) {
  options = opex(defaults, options);
  // your code
}

opex always returns a new object -- no more of those extra curly braces just to keep your shared defaults from changing: extend({}, defaults, options)
params are collapsed from left to right into the new object; right-most values override any to the left
non-object and non-function parameters are ignored, which allows for simple input sanitizing
consider:

var defaults = {};
function example(a, b, c) {
  var options = opex(defaults, a, b, c);
}

options will always be an object and opex will extend a new object with defaults and b even if a is null and c is an integer. It will also work if any parameter is a function which has had additional properties assigned to it, i.e. when a module wants to export a function but appends some helper data or functions to the exported function.

what about deep copy?

Only where it makes sense. opex is primarily indended to be used with JSON stuctures or a 'flat' object. Rather than use a flag (or always-on/off) like some implementations, opex decides whether to recurse on each property individually. Why? Deep copying can be dangerous. Best case, it's a little slower. Worst case? Non-enumerable properties get left behind while enumerable, this-dependent functions no longer behave as expected. To avoid these issues while still supporting deep copy for JSON-like structures (e.g. collapsing multiple config files based on application and environment), opex will only deep-copy simple objects and object literals. An object is deemed 'simple' when it's .__proto__ property is a direct reference to Object.prototype:

// which will recurse?
{}                // yes
new Object()      // yes
function x() { }  // no
[]                // no
5                 // no
{ y: [ 'foo' ] }  // yes, but y will not

You get the idea.. sound complicated? You'll find in most cases it's exactly what you would expect:

var opex = require('opex'),
  globalDefaults = {
    env: 'dev',
    log: {
      level: 'debug'
    }
  },
  appDefaults = {
    app: 'bar.com',
    log: {
      level: 'error'
    },
    key: 'bar'
  };

function App(options) {
  // options = {
  //   env: 'prod',
  //   signer: <Crypto.Signer instance>,
  //   customModule: <some custom utility>
  // }
  options = opex(globalDefaults, appDefaults, options);
  options.end;          // 'prod'
  options.log.level;    // 'error'
  options.key;          // 'bar'
  options.app;          // 'bar.com'
  options.singer;       // <Crypto.Signer instance> (non-deep copy)
  options.customModule; // <some custom utility> (non-deep copy)
}