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Asked: 2026-06-17T01:31:12+00:00

I have defined my select as below <select id=selProductType data-bind=options: productType , value: editProductType

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I have defined my select as below 

<select id="selProductType" data-bind="options: productType , value: editProductType , optionsText: 'Name'" />

Below is my code to fill the select in my view model

 // Loading combobox with Product Types
    $.getJSON("../RestService/Product/AllProductTypes",
      function (allData) {
          var mappedProductType = $.map(allData, function (item) {
              console.log(item.Id + ' ' + item.Name);
              return new productType(item);
          });
          self.productType(mappedProductType);

      });

When i initialise page i want to set default value to select. So i tried below

self.editProductType(4);

But it gives me TypeErrror saying object 4 has no method Id.

How to go about it. I have also gone through similar post in stackoverflow but no luck.

Knockout JS binding initial/default value of dropdown (select) list

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1 Answer

  1. Editorial Team

    If you don’t specify the :

    optionsValue: 'Id'

    in data-bind, the binding value in this case must be an object in productType array.

    You can select the default object:

    self.editProductType(self.productType()[2]);

    What is optionsValue?

    Similar to optionsText, you can also pass an additional parameter called optionsValue to specify which of the objects’ properties should be used to set the value attribute on the elements that KO generates. You can also specify a JavaScript function to determine this value. This function will receive the selected item as its only argument and should return a string to use for the element’s value attribute.

    Typically you’d only want to use optionsValue as a way of ensuring that KO can correctly retain selection when you update the set of available options. For example, if you’re repeatedly getting a list of “car” objects via Ajax calls and want to ensure that the selected car is preserved, you might need to set optionsValue to “carId” or whatever unique identifier each “car” object has, otherwise KO won’t necessarily know which of the previous “car” objects corresponds to which of the new ones.

    read more at: http://knockoutjs.com/documentation/options-binding.html

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