AngularJS: indexOf()

HTML

<div ng-controller="AppCtrl">
    <ul>
        <li ng-repeat="member in message.members">
            Member ID: {{ member.id }}
            <span ng-if="message.read_by.indexOf(member.id) > -1">Read</span>
        </li>
    </ul>
</div>

JavaScript

'use strict';

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

app.controller('AppCtrl', ['$scope', function ($scope) {
    
    $scope.message = {
        read_by: {1, 2, 3},
        members: [
            {id: 1},
            {id: 3},
            {id: 5}
        ];
    };
    $scope.classCodes="6-JEE-CHEM1";
    alert($scope.classCodes.indexOf("CHE"));
    if ($scope.classCodes.indexOf("CHE") >= 0) {
											alert(111);
		}
    
}]);