What is preventing me from binding the array index to a model in AngularJS with two-way binding?

I'm currently facing a challenge with a seemingly simple task: I have an array of string values that I want to link to a select element's options, and then connect the index of the chosen value to a variable. However, I have found that neither using ng-options nor regular options with ng-repeat fully accomplishes this task. The latter method works only after selecting some values, but does not bind with the initially set value when the page is loaded.

You can see an example of this issue in action on Codepen: http://codepen.io/modo_lv/pen/xGYQjM (click on "View Compiled" to view the pure HTML and JavaScript code). Pay attention to how both dropdowns are initially empty despite having a pre-set value. Additionally, selecting an option in the first dropdown results in unsetting the initial value.

javascriptangularjsdata-binding

Answer №1

Unable to bind it as $index is not defined for ngOptions, it's specific to ngRepeat. To get the index of the option, you can use the Array.prototype.indexOf method:

<select ng-model="testModel" 
        ng-options="labels.indexOf(label) as label for label in labels">
</select>

Example: http://codepen.io/anon/pen/MwBXBx

Answer №2

I am facing an issue with binding an array of string values to a select element's options and trying to bind the index of the selected value to a variable.

Unfortunately, neither using ng-options nor regular options with ng-repeat seems to be providing a complete solution for this problem.

The reason why ng-options is not working is because you are attempting to use $index with it (which only works with ng-repeat). To resolve this, you can modify your code to work with ng-options by replacing:

ng-options="$index as label for label in labels"

with:

ng-options="labels.indexOf(label) as label for label in labels"

Similarly, ng-repeat is not functioning properly because you are using $index on ng-value without an associated index in ng-model.

To rectify this issue and make your code compatible with ng-repeat, you can simply utilize ng-selected in the option tag like so:

<option  ng-repeat="label in labels" ng-selected = "{{label == testVal}}"  ng-value="$index">
    {{label}}
</option>

You can find the updated version of your code on this plunkr link.

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