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Knockoutjs default if empty

I have been working on a big project recently involving knockoutjs and have learnt so much about this data binding MVVM library. It is a well supported JavaScript framework with a large community of users, so there is always a solution to a problem. However I came across a little problem, not with knockoutjs, but with how IE handles empty <span> tags.

##The Problem

Basically, when IE8 (and presumably IE6+7) was rendering empty <span> tags, it was ignoring the min and max height styling. So if I had a property within my View Model that was an empty string, it would break the layout of my UI slightly. As a result, I needed a way of passing in a default “if empty” value which would be used instead of the property value.

There is one way to provide some default value to a peroperty by using knockoutjs extenders (see http://stackoverflow.com/a/10577446/177988) however in my situation the data which is being bound is a dynamically loaded json array.

##The Solution

I made use of knockout’s custom bindings to create a binding handler which would check the value, and then update the text.

ko.bindingHandlers.defaultIfEmpty = {
    init: function (element, valueAccessor, allBindingsAccessor, viewModel, bindingContext) {                
        var rawValue = ko.utils.unwrapObservable(valueAccessor());
        if (rawValue == "") {                    
            if (allBindingsAccessor().defaultText != undefined) {
                allBindingsAccessor().text = allBindingsAccessor().defaultText;
            } else {
                console.log('ko.bindingHandlers.defaultIfEmpty defaultText not provided.');

About Me

Tim James I'm Tim, a web applications developer from Glasgow, Scotland. Currently working for Kingfisher Systems Ltd, building bespoke systems within the Car Auction industry.

  • C#
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  • .NET MVC
  • Web API
  • Razor
  • HTML5
  • CSS3
  • jQuery
  • WCF
  • SQL
  • knockout.js
  • Angularjs
  • AJAX
  • APIs
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