AngularJS Built-in directives ngOptions
Example
ngOptions is a directive that simplifies the creation of a html dropdown box for the selection of an item from an array that will be stored in a model. The ngOptions attribute is used to dynamically generate a list of <option> elements for the <select> element using the array or object obtained by evaluating the ngOptions comprehension expression.
With ng-options the markup can be reduced to just a select tag and the directive will create the same select:
<select ng-model="selectedFruitNgOptions"
ng-options="curFruit as curFruit.label for curFruit in fruit">
</select>
There is anther way of creating select options using ng-repeat, but it is not recommended to use ng-repeat as it is mostly used for general purpose like, the forEach just to loop. Whereas ng-options is specifically for creating select tag options.
Above example using ng-repeat would be
<select ng-model="selectedFruit">
<option ng-repeat="curFruit in fruit" value="{{curFruit}}">
{{curFruit.label}}
</option>
</select>
Lets see the above example in detail also with some variations in it.
Data model for the example:
$scope.fruit = [
{ label: "Apples", value: 4, id: 2 },
{ label: "Oranges", value: 2, id: 1 },
{ label: "Limes", value: 4, id: 4 },
{ label: "Lemons", value: 5, id: 3 }
];
<!-- label for value in array -->
<select ng-options="f.label for f in fruit" ng-model="selectedFruit"></select>
Option tag generated on selection:
<option value="{ label: "Apples", value: 4, id: 2 }"> Apples </option>
Effects:
f.label will be the label of the <option> and the value will contain the entire object.
<!-- select as label for value in array -->
<select ng-options="f.value as f.label for f in fruit" ng-model="selectedFruit"></select>
Option tag generated on selection:
<option value="4"> Apples </option>
Effects:
f.value (4) will be the value in this case while the label is still the same.
<!-- label group by group for value in array -->
<select ng-options="f.label group by f.value for f in fruit" ng-model="selectedFruit"></select>
Option tag generated on selection:
<option value="{ label: "Apples", value: 4, id: 2 }"> Apples </option>
Effects:
Options will be grouped based on there value. Options with same value will fall under one category
<!-- label disable when disable for value in array -->
<select ng-options="f.label disable when f.value == 4 for f in fruit" ng-model="selectedFruit"></select>
Option tag generated on selection:
<option disabled="" value="{ label: "Apples", value: 4, id: 2 }"> Apples </option>
Effects:
"Apples" and "Limes" will be disabled (unable to select) because of the condition disable when f.value==4. All options with value=4 shall be disabled
<!-- label group by group for value in array track by trackexpr -->
<select ng-options="f.value as f.label group by f.value for f in fruit track by f.id" ng-model="selectedFruit"></select>
Option tag generated on selection:
<option value="4"> Apples </option>
Effects:
There is not visual change when using trackBy, but Angular will detect changes by the id instead of by reference which is most always a better solution.
<!-- label for value in array | orderBy:orderexpr track by trackexpr -->
<select ng-options="f.label for f in fruit | orderBy:'id' track by f.id" ng-model="selectedFruit"></select>
Option tag generated on selection:
<option disabled="" value="{ label: "Apples", value: 4, id: 2 }"> Apples </option>
Effects:
orderBy is a AngularJS standard filter which arranges options in ascending order(by default) so "Oranges" in this will appear 1st since its id = 1.
All <select> with ng-options must have ng-model attached.
