Unexpected Response from Server when updating SharePoint ListItem via JSOM

These days I am working a lot on the client-side of things. So I starting a couple of months ago writing my first lines of JavaScript with JSOM (Javascript (Client)-Side Object Model).

I wrote a small method to create list items in a list (listTitle) based on a collection/ list of properties (properties) and their respective values. Here it is:

function createListItem(listTitle, properties) {
    var d = $.Deferred();
    try {
        var ctx = SP.ClientContext.get_current();
        var oList = ctx.get_web().get_lists().getByTitle(listTitle);

        var itemCreateInfo = new SP.ListItemCreationInformation();
        oListItem = oList.addItem(itemCreateInfo);

        for (var i = 0; i < properties.length; i++) {
            var prop = properties[i];
            oListItem.set_item(prop.Key, prop.Value);
        }

        oListItem.update();
        ctx.load(oListItem);
        var o = { d: d, ListItem: oListItem, List: listTitle };
        ctx.executeQueryAsync(
        function () {
            o.d.resolve(o.ListItem);
        },
        function (sender, args) {
            o.d.reject("Could not create list item in list " + o.List + " - " + args.get_message());
        });
    } catch (Exception) {
        console.log(Exception.message);
    }
    return d.promise();
}

function updateListItem(listTitle, properties) {
  var d = $.Deferred();
  try {
        var d = $.Deferred();
        var ctx = SP.ClientContext.get_current();
        var oList = ctx.get_web().get_lists().getByTitle(listTitle);

        oListItem = oList.getItemById(id);

        for (var i = 0; i < properties.length; i++) {
            var prop = properties[i];
            try {
                oListItem.set_item(prop.Key, prop.Value);
            } catch (Exception) {
                console.log(prop.Key + ' ' + prop.Value);
                console.log(Exception.message);
            }
        }
        oListItem.update();
        //ctx.load(oListItem);
        var o = { d: d, ListItem: oListItem, List: listTitle, p: properties };
        ctx.executeQueryAsync(
            Function.createDelegate(o, 
        function () {
            o.d.resolve(o.ListItem);
        }),
        Function.createDelegate(o, 
        function (sender, args) {
            o.d.reject("Could not update list item in list " + o.List + " - " + args.get_message());
        }));
    } catch (Exception) {
        console.log(Exception.message);
    }
  return d.promise();
}

So what happened when I executed while editing another item in a different list? When I debugged using Chrome (my browser of choice when writing JavaScript – never used it before that, interestingly…) I received an error “unexpected response from the server”.

I figured out that there are two key lines in this code.

var ctx = SP.ClientContext.get_current();

and

ctx.load(oListItem);

The first line was actually not responsible for the error message in my case but if you use var ctx = new SP.ClientContext(url); you may encounter this error message, as well. You should always use the current client context, when using JSOM, similar to the best practice guidelines for opening webs on server-side (SSOM [Server-Side Object Model]).

The second line was actually the issue in my code.

When creating an item I need to load the item into the context afterwards (or the error will show up even if the item is created correctly).

When updating an item the item may not be loaded into the context afterwards (or the error will show up even if the item is updated correctly).

It kind of makes sense, because when creating an item you are actually sending an SP.ListItemCreationInformation to the server. When updating an item I already have my listitem object. Why would I need to load all the other information afterwards?

So once I removed the line from the update method the code no longer evaluated to fail and the error message disappeared.

So for the experts among you this may be old news, but I actually needed to think about this for a few minutes before I figured it out, so I thought it was well worth blogging about. Especially since I haven’t blogged for quite some time.

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