Can I Use A Javascript Array Object As An Argument In A Function? How?

So I'm trying to create a function that takes in an array (I guess it's more of a JSON object, or so we were told) object and returns a value based on that array, but I keep getting an error, so I'm pretty certain I'm doing this wrong.

I'm fairly new at JavaScript so go easy on me. Also, I found this thread which is similar to the question I'm asking, but I don't quite understand THAT question (and therefore it's answers).

Here's a sample of the object we're given:

var returned_json =  {
    "nike_runs": [
        {
            "start_time": "2011-03-11T19:14:44Z",
            "calories": 12.0,
            "distance_miles": "0.10",
            "total_seconds": 288.0,
            "average_pace":"50.47"
        },
        {
            "start_time": "2011-03-11T19:41:25Z",
            "calories": 7.0,
            "distance_miles": "0.06",
            "total_seconds": 559.0,
            "average_pace": "165.1开发者_开发百科9"
        },
        {
            "start_time": "2011-03-11T20:27:45Z",
            "calories": 197.0,
            "distance_miles": "1.63",
            "total_seconds": 8434.0,
            "average_pace": "86.22"
        },
        ...
    ]
}

Here's my code:

function getExp (returned_json) {
    var exp;
    for (var i = 0; i <= returned_json.nike_runs.length; i++) {
        exp += returned_json.nike_runs[i].calories;
    }
    return exp;
}

It returns an error:

TypeError: returned_json.nike_runs[i] is undefined

I figured this has to do with the fact I'm not defining the type of object I want to pass into the function, but my research tells me that doesn't matter.

Help? :(

Thanks.

---

Use i < returned_json.nike_runs.length, not i <= returned_json.nike_runs.length.

Edit: While you’re at it, you better define a starting value for exp too.