Undefined error in reading the property of object

Question

Please help to solve the undefined error coming in my console while running the below code

Please see this JSbin also http://jsbin.com/ONOwujA/1/edit

data = [
    {key:"home",value:"hk1"},
    {key:"home",value:"hk2"},
    {key:"home",value:"hk3"},
    {key:"home",value:"hk4"},
    {key:"product",value:"pk1"},
    {key:"product",value:"pk2"},
    {key:"product",value:"pk3"},
    {key:"product",value:"pk4"},
    {key:"service",value:"sk1"},
    {key:"service",value:"sk2"},
    {key:"service",value:"sk3"},
    {key:"service",value:"sk4"}
];

myFilteredKey=[];
for(i=0;i<=data.length;i++){

    if(myFilteredKey.indexOf(data[i].key)!=-1){
        myFilteredKey.push(data[i].key);
        console.log(data[i].key);
    }
}

Answer 1

Use i < data.length . If the length is 3 , the maximum index is 2 .

Another problem with your code is that no element will be added to myFilteredKey . Since the array is already empty, no element will satisfy the condition myFilteredKey.indexOf(data[i].key)!=-1 . Maybe you want to use === -1 instead, ie check whether the element is not in the array rather than whether it's in the array.