Question

The following function results in the response variable being null in Chrome and Safari but not Firefox.

function updatePage(response){ // This argument differs by browser

    response = jQuery.parseJSON(response);

    for(var i=0; i<response.length; i++){
        // conduct magic
    };

};

Error:

Uncaught TypeError: Cannot read property 'length' of null

This is because feeding jQuery.parseJSON() anything but a JSON string returns null. It seems Chrome and Safari automatically parse JSON without explicitly being requested. If I test the “response” argument before trying to parse it with jQuery, it’s already a JSON object in both Chrome and Safari. However, in Firefox it’s still a string.

The only solution I’ve come up with to handle this across browsers is to determine if “response” has already been parsed by checking its constructor:

function updatePage(response){

    if(response.constructor === String){
        response = jQuery.parseJSON(response);
    };

    for(var i=0; i<response.length; i++){
        // conduct magic
    };

};

Am I missing something or is this the only way to handle this currently? Seems like jQuery.parseJSON would detect the user-agent and just return the argument as-is in the case of Chrome/Safari.

Pertinent information

• This is jQuery 1.6.1
• The response Content-Type from the server is application/json
• The response argument is originating from your standard jQuery AJAX call:

---

$.ajax({
    url: API_URL + queryString + '&limit=' + limit,
    type: 'GET',
    cache: false,
    context: document.body,
    success: updatePage,
    error: function(err){
        console.log('ERROR: ' + err);
    }
});

Answer 1

It’s not Chrome or Safari, it’s jQuery that does the parsing if it sees the appropriate Content-Type on the response. (Update: And the Content-Type you’ve added to the question is correct.) I can’t immediately see why it wouldn’t be doing it on Firefox.

You can force it to always do the parsing by adding dataType: 'json' to your call, details in the jQuery.ajax docs. Then you wouldn’t call parseJSON at all, response would already be the deserialized object.