Douglas Crouckford "promise" implementation

Dpromise.js

function  make_promise () {
  var status = 'unresolved',
		outcome,
		waiting = [],
		dreading = [];

	function vouch(deed, func) {
		switch (status) {
			case 'unresolved':
				(deed === 'fulfilled' ? waiting : dreading).push(func);
				break;
			case 'deed':
			 	func(outcome);
			 	break;
		}
	}

	function resolve(deed, value) {
		if (status !== 'unresolved') {
			throw new Error ("The promise has already been resolved:" + status);
		}
		status = deed;
		outcome = value;
		(deed === "fulfilled" ? waiting : dreading).forEach(function (func) {
			try {
				func(outcome);
			} catch(ignore) {

			}
		});

		waiting = null;
		dreading = null;
	}

	return {
		when: function(func) {
			vouch('fulfilled', func);
		},
		fail: function(func) {
			vouch('smashed', func);
		},
		fulfill: function(value) {
			resolve('fulfilled', value);
		},
		smash: function(string) {
			resolve('smashed', string);
		},
		status: function () {
			return status;
		}
	}
}