Javascript loop through object array?

It appears you may just have missed the "messages" property in the data, so the loop is likely iterating the root Object rather than the Array:

for (var key in data.messages) {
    var obj = data.messages[key];
    // ...
}

Unless data was set to messages before the given snippet.

Though, you should consider changing that to a normal for loop for the Array:

for (var i = 0, l = data.messages.length; i < l; i++) {
    var obj = data.messages[i];
    // ...
}

You can use forEach method to iterate over array of objects.

data.messages.forEach(function(message){
    console.log(message)
});

Refer: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/forEach

In your script, data is your whole object.

key is "messages", which is an array you need to iterate through like this:

    for (var key in data) {
       var arr = data[key];
       for( var i = 0; i < arr.length; i++ ) {
           var obj = arr[ i ];
           for (var prop in obj) {
               if(obj.hasOwnProperty(prop)){
                   console.log(prop + " = " + obj[prop]);
               }
           }
       }
    }