JSFiddle - React, Tailwind, and code Playground

HTML

<div ng-controller="Ctrl">
    <select ng-init="sid = 473" ng-model='sid'
      ng-options="y.id as ( y.id + ' - ' + y.title) for y in arr">
    </select>
    <input type="hidden" name="size" value="{{sid}}"/>
    {{ sid }}
    <button ng-click='sid=474'>change to 474</button>
</div>

JavaScript

var app =angular.module('app', []);

function Ctrl($scope){
    $scope.arr = [{"id":472,"title":"aa"},{"id":473,"title":"bb"},{"id":474,"title":"cc"}];
}