Detecting if a property value exists in an array of objects

Question

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:

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);

Anurag · Accepted Answer · 2012-07-30 00:17:26Z

3

for (x in y) is not the right construct to iterate through objects in an array. It is meant to be used for iterating through keys of an object only.

So what is happening is that instead of getting the two Entity objects, the member variable is referring to the index of those objects which is 1 and 2 respectively. The correct way to iterate through those objects is:

for(var i = 0; i < members.length; i++) {
    EntityID == members[i].EntityID;
}

answered Jul 30, 2012 at 0:17

Anurag

142k37 gold badges223 silver badges262 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

Newtang · Accepted Answer · 2012-07-30 00:17:37Z

3

The problem is your for...in loop. You should only use for...in when iterating over properties in an object, not through items of an array.

If you replace this loop with the following, you should be fine:

for(var i=0,len=members.length; i<len; ++i){
     var member = members[i];
     //the rest

answered Jul 30, 2012 at 0:17

Newtang

6,58411 gold badges54 silver badges72 bronze badges

Collectives™ on Stack Overflow

Detecting if a property value exists in an array of objects

2 Answers 2

Comments

Comments

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

Comments

Comments

Related