dist/lib/before.js
function before(fn, callback) {
    return function () {
        for (var _len = arguments.length, args = Array(_len), _key = 0; _key < _len; _key++) {
            args[_key] = arguments[_key];
        }

        if (callback.apply(this, [fn.bind(this)].concat(args)) !== false) {
            return fn.apply(this, args);
        }
    };
}
function before(fn, callback) {
    return function () {
        for (var _len = arguments.length, args = Array(_len), _key = 0; _key < _len; _key++) {
            args[_key] = arguments[_key];
        }

        if (callback.apply(this, [fn.bind(this)].concat(args)) !== false) {
            return fn.apply(this, args);
        }
    };
}
Returns a method decorator taking a callback, which will be invoked
before the execution of the decorated function, *unless* the callback
returns `false`.

@param fn a function to be decorated
@param callback a handler to be invoked beforehand