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Why does $.getJSON silently fail?

Posted by: admin November 29, 2017 Leave a comment

Questions:

It seems very inconvenient that jQuery’s $.getJSON silently fails when the data returned is not valid JSON. Why was this implemented with silent failure? What is the easiest way to perform getJSON with better failure behavior (e.g. throw an exception, console.log(), or whatever)?

Answers:

you can use

        function name() {
            $.getJSON("", function(d) {
                alert("success");
            }).done(function(d) {
                alert("done");
            }).fail(function(d) {
                alert("error");
            }).always(function(d) {
                alert("complete");
            });
        }

If you want to see the cause of the error, use the full version

function name() {
    $.getJSON("", function(d) {
        alert("success");
    }).fail( function(d, textStatus, error) {
        console.error("getJSON failed, status: " + textStatus + ", error: "+error)
    });
}

If your JSON is not well-formed, you will see something like

getJSON failed, status: parsererror, error: SyntaxError: JSON Parse error: Unrecognized token '/'

If the URL is wrong, you will see something like

getJSON failed, status: error, error: Not Found

If you are trying to get JSON from another domain, violating the Same-origin policy, this approach returns an empty message. Note that you can work around the Same-origin policy by using JSONP (which has it’s limitations) or the preferred method of Cross-origin Resource Sharing (CORS).

Questions:
Answers:

Straight from the documentation:

Important: As of jQuery 1.4, if the JSON file contains a syntax error, the request will usually fail silently.

As the documentation page says, getJSON is simply a shorthand method for

$.ajax({
    url: url,
    dataType: 'json',
    data: data,
    success: callback
});

To get failure behavior, you can use $.ajax like this:

$.ajax({
    url: url,
    dataType: 'json',
    data: data,
    success: callback,
    error: another callback
});

Questions:
Answers:

You can use $.ajax instead, and set the dataType options to “json”. From the documentation:

“json”: Evaluates the response as JSON
and returns a JavaScript object. In
jQuery 1.4 the JSON data is parsed in
a strict manner; any malformed JSON is
rejected and a parse error is thrown.
(See json.org for more information on
proper JSON formatting.)

Questions:
Answers:

You should have a look at the docs for this API… it has a .error on it.

http://api.jquery.com/jQuery.getJSON/

Questions:
Answers:

If you’re requesting JSONP as the response, you will get a silent fail if there is no response (e.g. network outage). See this thread for details.