Unexpeced token error when setting contentType to application/json

Question

I am sending data using AJAX POST. The data is JSON format. See below. However, I keep getting 'Unexpected token u in JSON at position 0'. Why is this happening? The reason I am setting contentType here is so that the Boolean field checked does not get converted to string.

var data = { "user": "tom", "number": 9, "checked": false } $.ajax({ url: url, method: "POST", data: data, contentType: 'application/json', dataType: 'json', beforeSend: function (xhr) { xhr.setRequestHeader ("Authorization", "Basic " + btoa(username + ":" + password)); }, success: function (success) { console.log("success"); } });

where do you get the error? When the javascript runs or when you recieve the answer? — Liora Haydont
– Liora Haydont, Commented Dec 7, 2017 at 2:17
@LioraHaydont previously I did not have contentType: 'application/json' and the backend is treating the Boolean like a string, so I read that I should set it to avoid this issue. Which I did, and now it won't even get sent to the backend server — b11
– b11, Commented Dec 7, 2017 at 2:19

charlietfl · Accepted Answer · 2017-12-07 02:27:20Z

1

When you use contentType: 'application/json', you need to stringify the data yourself:

data: JSON.stringify(data),

As for the error that seems like a response problem. Inspect the actual request in browser dev tools network and see what is actually contained in the reponse body

answered Dec 7, 2017 at 2:27

charlietfl

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1 Comment

nnnnnn Over a year ago

The quoted error would be happening server side (and perhaps then included in the response), because the server is receiving the data as user=tom&number=9&checked=false so the first character in the request body is the "u" from "user" and obviously that can't be parsed as JSON.

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