Question

I have a JSON object which is generated by PHP. It’s an object with a set of dates. It has the timeStamp and then a formatted version of the date. How would I iterate through this in jQuery?

{
  "dates":[
    {
      "timeStamp": 1317596400,
      "formattedDate": "Mon 03 October 2011"
    },
    {
      "timeStamp": 1317682800,
      "formattedDate": "Tue 04 October 2011"
    },
    {
      "timeStamp": 1317855600,
      "formattedDate": "Thu 06 October 2011"
    }
  ]
}

I’ve tried:

for (var i in data) { 
  alert(data.dates[i].timeStamp); 
};

for (var i in data) { 
  alert(data[i].dates.timeStamp); 
};

and

for (var i in data) { 
  alert(data.dates.timeStamp[i]); 
};

Answer 1

Since you tagged your question as a jquery one, you should use $.each because it’s jquery’s iterator function:

$.each(data.dates, function(index, element) {
    alert(element.timeStamp); 
});

If you want to stick to the for in syntax (which i see you’ve tried), a solution might be :

for(var key in data.dates) {
     alert(data.dates[key].timeStamp); 
} 

But beware that the for in syntax may do more than you think it does: it iterates over the properties inherited from the prototype too, so it might be usefull to make sure you iterate only on the object instance properties:

for(var key in data.dates) {
    // if it's not something from the prototype
    if(data.dates.hasOwnProperty(key)) {
        alert(data.dates[key].timeStamp); 
    }
} 

update
Another elegant way is to use the Object.keys method that returns an array containing all the keys in the targeted object to iterate over all the object’s properties:

for(var i=0, keys=Object.keys(data.dates), l=keys.length; i<l; i++) {
    alert(data.dates[i].timeStamp);
}