knockoutjs binder for bootstrap typeahead

ko.typeahead.binder.js

// FYI YMMV this was just a first pass and I know it has some issues at times that I need to workout

// usage
// source: a function that takes the query (text entered by user) and a callback (process), if source is synchronous it should return the results and ignore the callback, otherwise it should return nothing and use the callback to return the results
// selectedId: the model property to bind the id to
// value: the model property to bind the text value of the selection to
// data-bind="typeahead: { source: App.view.targets.typeAheadSource, selectedId: target._id  }, value: target.name"

// note I also use this little helper class to wrap up all this functionality
// it takes a url to query the results for asynchrnous data sets and has an init method to call to query the data initially.
function TypeAhead(url) {
    var self = this;
    self.data = ko.observableArray([]);
    self.typeAheadSource = function () {
        return self.data();
    };
    self.init = function () {
        $.ajax({
            url: url,
            dataType: 'json'
        }).success(self.data);
    };
    return self;
}


require(['knockout', 'jquery.elastic'], function (ko) {
    ko.bindingHandlers.typeahead = {
        init: function (element, valueAccessor, allBindingsAccessor, viewModel, bindingContext) {
            var parameters = ko.toJS(valueAccessor());
            var defaults = {
                items: 10,
                minLength: 0
            };
            var source = parameters.source;
            var queryResults = {};
            parameters.source = function (query, process) {
                var processText = function (results) {
                    results.forEach(function (r) { queryResults[r.text] = r._id});
                    process(results.map(function (r) { return r.text; }));
                }
                var synchronousResults = source(query, processText);
                if (!synchronousResults) {
                    return;
                }
                return processText(synchronousResults);
            }
            allBindingsAccessor().value.subscribe(function (selectedText) {
                valueAccessor().selectedId(queryResults[selectedText])
            })
            $(element).typeahead($.extend(defaults, parameters));
        }
};
});