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                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>





                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());