shriek shriek - 1 year ago 318
Javascript Question

Selecting default option value with knockout

I'm trying to select a default select option based on one of the property with which I'm populating my select option.

This code is copied straight from @rneimeyer's fiddle. I did tweak it to do what I wanted to do.

So, I have choices as my observableArray.

var choices = [
{ id: 1, name: "one", choice: false },
{ id: 2, name: "two", choice: true },
{ id: 3, name: "three", choice: false }

function ViewModel(choices, choice) {
this.choices = ko.observableArray(choices);

The difference between rneimeyer's fiddle and mine is that I have
property added on my object inside the observableArray instead of having a separate observable for the option that we want to be default.

Here's the fiddle on my attempt.

Now I'm checking in my select element tag whether the
attribute is true or not. And if it is then I want to set the
to the
attribute so that it becomes the default.

<select data-bind="options: choices, optionsText: 'name', value: choice"></select>

I've tested this with simple data model in my fiddle here as well which is working just as I wanted.

I guess what my real query is how to check
property in the data-bind. I see that
is being able to access the
property just fine. Not sure why it isn't same for
property in

Answer Source

I might have misdirected to some people. Also, I apologize for not mentioning the version that I'm using. I'm currently using Knockout 3.0.0 (you'll see why this is important later)

Also, just to note that I'm not saying @XGreen's method is wrong but that wasn't exactly what I was looking for and this might be due to my poor explanation.

Let me first try to clarify what I was trying to accomplish. First of all, I will be having an array of object with the information for the options.

 { id: 1, name: "one", choice: false },
 { id: 2, name: "two", choice: true },
 { id: 3, name: "three", choice: false }

Now, what I wanted to do was to data-bind select option to that array with choice true being the default selected one.

I'm not intending to create any extra observable except the array itself which is going to be an observableArray.

After much research I finally found optionsAfterRender attribute for options property in Knockout's Docs.

<select data-bind="options: choices, 
                   optionsValue: 'name',
                   optionsAfterRender: $root.selectDefault">

So what optionsAfterRender really does is, on each array element it calls custom function which I've set to check if the choice is true or not and make the value of select option that which has the true.

Do note that ko.applyBindingsToNode does not work on version 2.2.0 which I had in my original fiddle.

function ViewModel(choices) {
   this.choices = ko.observableArray(choices);
    this.selectDefault = function(option,item){
            ko.applyBindingsToNode(option.parentElement, {value:}, item);
ko.applyBindings(new ViewModel(choices));

And here's the fiddle for it.

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