title: Detecting if a property value exists in an array of objects
body: <p>I am trying to check if a 'member' object with a specific 'ID' already exists in the 'members' array of a container 'EntityGroup' object. why doesn't the following EntityGroup.idExists(id) work:</p>
  
  <pre><code>EntityGroup = function() {
      this.members = []; // intention is for this to hold 'Entity' objects
      this.classType = null; // what class of entities does it hold
  };
  EntityGroup.prototype = {
      addEntity: function(entityType, EntityID) {
  
          // TODO implement .idExists() check here 
          // dont add new member if the id does exist
          this.members.push(new Entity(entityType, EntityID))
  
      },
  
      idExists: function(EntityID) {
  
          var idExists = false,
              member, 
              members = this.members;
  
          for (member in members) {
  
              if (EntityID == member.EntityID) {
                  idExists = true;
                  break;
              } else {
                  continue;
              }
          }
          return idExists;
      }
  };
  
  Entity = function(entityType, EntityID) {
      this.EntityID = EntityID;
      this.entityType = entityType;
  };
  
  g = new EntityGroup();
  g.addEntity("Person", 1);
  g.addEntity("Person", 2);
  
  console.log(g.idExists(1)); // returns false which is not expected
  console.log(g.members); 
  </code></pre>