How to get JSON column names in Javascript

Question

I have the following JSON response:

{
"d": {
    "results": [
        {
            "__metadata": {
                "id": "c55209ae-2af9-4514-ab02-67f222903f6d",
                "uri": "https://site-GUID.sharepoint.com/sites/dev/MyApp/_api/Web/Lists(guid'46f26a73-0079-4662-ae99-7f4be03e26a4')/Items(1)",
                "etag": "\"1\"",
                "type": "SP.Data.LstDoelenListItem"
            },
            "scDoelnaam": "Hoofddoel Afdeling",
            "scDoellevel": 1
        },
        {
            "__metadata": {
                "id": "7e79ab8a-e550-4694-87d4-26d6f5bc6128",
                "uri": "https://site-GUID.sharepoint.com/sites/dev/MyApp/_api/Web/Lists(guid'46f26a73-0079-4662-ae99-7f4be03e26a4')/Items(2)",
                "etag": "\"1\"",
                "type": "SP.Data.LstDoelenListItem"
            },
            "scDoelnaam": "Subdoel 1",
            "scDoellevel": 2
        },
        {
            "__metadata": {
                "id": "c204acca-0362-4bd6-a66b-00236a2320cb",
                "uri": "https://site-GUID.sharepoint.com/sites/dev/MyApp/_api/Web/Lists(guid'46f26a73-0079-4662-ae99-7f4be03e26a4')/Items(3)",
                "etag": "\"1\"",
                "type": "SP.Data.LstDoelenListItem"
            },
            "scDoelnaam": "Subdoel 2",
            "scDoellevel": 2
        },
        {
            "__metadata": {
                "id": "b78b2416-7813-4e64-a920-f9ba377fa36d",
                "uri": "https://site-GUID.sharepoint.com/sites/dev/MyApp/_api/Web/Lists(guid'46f26a73-0079-4662-ae99-7f4be03e26a4')/Items(4)",
                "etag": "\"1\"",
                "type": "SP.Data.LstDoelenListItem"
            },
            "scDoelnaam": "Subdoel 3",
            "scDoellevel": 2
        }
    ]
}

}

I know how to retrieve the values once I know the column names, but how do I get the 2 column names "scDoelnaam" and "scDoellevel" with Javascript and assign them to variables??

Answer 1

The following REST endpoint demonstrates how to retrieve List resource with Fields and Items properties:

/_api/web/lists/getbytitle('<list title>')?$expand=items,fields

Example

var endpointUrl = _spPageContextInfo.webAbsoluteUrl + "/_api/web/lists/getbytitle('Documents')?$expand=items,fields";
getJson(endpointUrl)
.done(function(data)
{
    var fields = data.d.Fields.results; //get fields
    var items = data.d.Items.results; //get items
})
.fail(
function(error){
    console.log(JSON.stringify(error));
});

where

function getJson(url) 
{
    return $.ajax({       
       url: url,   
       type: "GET",  
       contentType: "application/json;odata=verbose",
       headers: { 
          "Accept": "application/json;odata=verbose"
       }
    });
}

Answer 2

The query _api/Web/Lists(guid'46f26a73-0079-4662-ae99-7f4be03e26a4')/Fields will give you the fields in the list. From the results you can get both the display name and the internal name of all the fields.