Angular injects “string:” before value in ng-options

Answer 1

This behavior is documented in the angular changelogs, as a breaking change for Angular 1.4-beta.0. https://github.com/angular/angular.js/blob/master/CHANGELOG.md#breaking-changes-17

Basically, in order to preserve duplicate checking within ng-options, if a list of primitive values are supplied to ng-options, the value's type is prepended to the value in order to create a unique hash key to track (this differs from earlier versions of angular, which would track by the index or the key of the item in the collection).

In practice, this should not affect most usages of ng-options. If it is important for you to preserve the value parameter of the dropdown, you can use the track by parameter in ng-options in order to provide an alternate key to be used for duplicate tracking.

Note that this differs from ng-repeat, in that ng-repeat cannot generate a surrogate key using this method, since it would affect the behavior of the repeated elements. Therefore if a duplicated list is passed to ng-repeat without a track by clause, ng-repeat will produce an error and not render the items, where ng-options is able to render the list.