Non-leaky implementation of Crockford's make_sealer

gistfile1.js

function make_sealer(){
	var cur = null, ret;

	return {
		sealer: function write(value){
			return function f(){
				if(f === cur)
					ret = value;
			};
		},

		unsealer: function read(box){
			ret = undefined;
			cur = box;
			box();
			cur = null;
			return ret;
		}
	};
}

var s = make_sealer();
var secret = s.sealer(42), magic = s.sealer("forty two");
print([secret, magic].map(s.unsealer));