Getting "Invalid JSON primitive" error from MVC AJAX call

Question

I've read every reference to "Invalid JSON primitive" with no success, so I have no choice but to post my own. I have reduced my code down to the bare minimum and am still getting the error. Here's the "bare minimum":

var dataObject = {
    'FirstName': $('#FirstName').val(),
    'LastName': $('#LastName').val()
};

$.ajax({
    type: 'POST',
    url: '@Url.Action("Submit", "Home")',
    contentType: 'application/json;',
    dataType: 'json',
    data: dataObject,
    success: function (result) {
        debugger;
        alert('Success');
    },
    error: function (response) {
        debugger;
        alert('Error');
    }
});

I have also tried replacing the dataObject with:

var dataObject = {
    'FirstName': 'ES',
    'LastName': 'Dictor'
};

Giving no change to my results.

No matter what I do I get (Chrome console):

response:
Object {readyState: 4, responseText: "<!DOCTYPE html>
↵<html>
↵    <head>
↵        <titl…nStep step, Boolean& completedSynchronously)
↵-->", status: 500, statusText: "Internal Server Error"}

and if I look at response.responseText I see:

<!DOCTYPE html>
<html>
    <head>
        <title>Invalid JSON primitive: FirstName.</title>

I believe I've tried everything at this point, so it's probably something simple that I'm just missing. Hoping that somebody can see what I can't.

@DavidTansey The HTML is just giving me the error .. if it wasn't failing I'd expect JSON. — ESDictor
– ESDictor, Commented Oct 6, 2015 at 16:07
We would need to see what your post does on the back end. It could be accessing a database incorrectly or referencing pages that don't exist something like that which could result in a internal server error. — Demodave
– Demodave, Commented Oct 6, 2015 at 16:08
@Demodave my assumption was that the "invalid json primitive" error meant that it wasn't getting that far. Am I incorrect? — ESDictor
– ESDictor, Commented Oct 6, 2015 at 16:10
@ESDictor -- sorry, I was not looking closely enough. Have you tried using JSON.stringify() on the data? Something like data: JSON.stringify(dataObject) ? — David Tansey
– David Tansey, Commented Oct 6, 2015 at 16:10
@DavidTansey earlier you mentioned the error being returned in HTML, not JSON. Based on that I commented out the "contentType" line and am now getting some success. Not sure if I'm 100% there yet, but I'm closer. — ESDictor
– ESDictor, Commented Oct 6, 2015 at 16:35

user3559349 · Accepted Answer · 2015-10-07 22:20:24Z

1

You posting back an object, not json, so you need to remove the contentType: 'application/json;', ajax option so that it uses the default (which is 'application/x-www-form-urlencoded; charset=UTF-8') Alternatively you need to use JSON.stringify() to convert the object to a JSON string.

Side note: It is not necessary to quote the property names. It can be

var dataObject = {
    FirstName: $('#FirstName').val(),
    ....

answered Oct 7, 2015 at 22:20

user3559349

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1 Comment

ESDictor Over a year ago

You are correct that it's not necessary to quote the property names, but it actually has no effect to do so. :)

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