A Pen by Rahul P Nath.

index.html

Enter a value and tab off and you will see the currency $ coming in automatically.
<p>Enter bid price: <input data-bind="value: formattedPrice"/></p>

IValueConverter.markdown

IValueConverter

This is an example for the blog post 'KnockoutJS for XAML Developers' - http://www.rahulpnath.com/blog/knockoutjs-for-xaml-developers/

A Pen by Rahul P Nath on CodePen.

License.

script.js

function MyViewModel() {
  this.price = ko.observable(25.99);

  this.formattedPrice = ko.computed({
    // Similar to Convert function on IValueConverter
    read: function () {
      return '$' + this.price().toFixed(2);
    },
    // Similar to ConvertBack on IValueConverter
    write: function (value) {
      // Strip out unwanted characters, parse as float, then write the raw data back to the underlying "price" observable
      value = parseFloat(value.replace(/[^\.\d]/g, ""));
      this.price(isNaN(value) ? 0 : value); // Write to underlying storage
    },
    owner: this
  });
}

ko.applyBindings(new MyViewModel());