Knockout.js: time input format and value restriction

Here is a thread with a few different techniques to keep the value numeric: https://groups.google.com/d/topic/knockoutjs/SPrzcgddoY4/discussion

One option is to push this concern into your view model and create a numericObservable to use instead of a normal observable. It might look like:

ko.numericObservable = function(initialValue) {
    var _actual = ko.observable(initialValue);

    var result = ko.dependentObservable({
        read: function() {
            return _actual();
        },
        write: function(newValue) {
            var parsedValue = parseFloat(newValue);
            _actual(isNaN(parsedValue) ? newValue : parsedValue);
        }
    });

    return result;
};

Sample: http://jsfiddle.net/rniemeyer/RJbdS/

Another option is to handle this with a custom binding. Instead of using the value binding, you can define a numericValue binding and use it instead. It could look like:

ko.bindingHandlers.numericValue = {
    init : function(element, valueAccessor, allBindings, data, context) {
        var interceptor = ko.computed({
            read: function() {
                return ko.unwrap(valueAccessor());
            },
            write: function(value) {
                if (!isNaN(value)) {
                    valueAccessor()(parseFloat(value));
                }                
            },
            disposeWhenNodeIsRemoved: element 
        });

        ko.applyBindingsToNode(element, { value: interceptor }, context);
    }
};

Sample: http://jsfiddle.net/rniemeyer/wtZ9X/