Question

In knockout.js I have a very standard field that looks like this:

<label data-bind="text: JobTitle"></label>

What I’d like is to have a default value specified in here if the text value is null, for example “No Job Title Specified”.

Is this possible to do in knockout.js?

Thanks.

Answer 1

So I’m guessing you want a real default value and not just a placeholder text. Here’s a way to do that with an extender;

ko.extenders.defaultIfNull = function(target, defaultValue) {
    var result = ko.computed({
        read: target,
        write: function(newValue) {
            if (!newValue) {
                target(defaultValue);
            } else {
                target(newValue);
            }
        }
    });

    result(target());

    return result;
};

var viewModel = function() {
   this.someValue = ko.observable().extend({ defaultIfNull: "some default" });
};

ko.applyBindings(new viewModel());

http://jsfiddle.net/madcapnmckay/aTMpp/

Hope this helps.