JSON.parse causes "Uncaught SyntaxError: Unexpected token u"

Question

I have:

<input type="hidden" id="notifications" value="@ViewBag.Notifications" />

When I put a breakpoint on this line and check the value, I see that the value is:

[{"id":"42647","isRead":0,"MessageType":3},{"id":"fsh3hg","isRead":0,"MessageType":2}]

I want to parse this value in JavaScript when the page loads, so I wrote:

var notifications = document.getElementById('notifications').value;
alert(notifications); // it prints undefined
alert(document.getElementById('notifications')); // it prints: Object HtmlSpanElement

var parsedNotifications;

if (notifications != '') {
    parsedNotifications = JSON.parse(notifications);
}

but I get the error "Uncaught SyntaxError: Unexpected token u" on the following line:

parsedNotifications = JSON.parse(notifications);

Why does this error occur?

The value is not being output correctly. here is a fiddle with the value correct and it is working: jsfiddle.net/A5Kf7 — Daniel Moses
– Daniel Moses, Commented Jul 23, 2013 at 18:26
you are doing some mistake while parsing...this error mostly appears when we use json.parse with an undefined object... — HIRA THAKUR
– HIRA THAKUR, Commented Jul 23, 2013 at 18:26

Michael Liu · Accepted Answer · 2013-07-23 19:42:54Z

4

You wrote:

alert(document.getElementById('notifications')); // it prints: Object HtmlSpanElement

In the comment, HtmlSpanElement is a clue that something's wrong. Apparently, your page has a <span> whose id is the same as that of your hidden <input>, so document.getElementById finds the wrong element, and value returns undefined because a <span> doesn't have a value.

Change the id of the <span> to something other than "notifications", and your code should work.

edited Jul 23, 2013 at 19:42

answered Jul 23, 2013 at 19:31

Michael Liu

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Comments

milestyle · Accepted Answer · 2013-07-23 19:11:36Z

0

So we know that document.getElementById('notifications') is there, which means that the only problem is it can't find the input value. Sometimes external libraries will block the input of hidden elements. Strip your page of everything except for the the code you showed us, and then try adding in the other libraries you've included one-by-one till you find the problem.

answered Jul 23, 2013 at 19:11

milestyle

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