Question

I’m working in an application that sends to me a XML so I can work with the data in it. But now the application will send not only a XML, but also a JSON, depending on other variables.

Is there any way that I can verify if what has been sent is a JSON? Something equivalent to typeof or instanceof that will tell me that string is a JSON?

Edit: I’m giving maintenance in this application that has been built using a very, very bad programmed framework. Right now my “data” is the return of a function and I’m unable to get the Content-Type without refactoring good part of the framework – what would take me months – and I don’t have this time right now.

Right now:

ajax.request('POST',function(data){
    xml = loadXML(data); // It's always a XML, so I simply load it.
    ...
    ..
})

What I need:

ajax.request('POST',function(data){
    if(valueCanBeJSON(data)){ // It's not always a XML. How can I do this verification?
        json = eval('('+data+')');
    }else{
        xml = loadXML(data);
        ...
        ..
    }
})

Answer 1

As @Gumbo commented, you can check the Content-Type HTTP response header field. Alternately, you could try to parse it — though don’t use eval(). Use JSON.parse(). If you’re using jQuery, $.parseJSON() or just $.ajax() (without specifying the data-type) will also work.

ajax.request('POST', function(data) {
    var isJSON;
    try {
        data = JSON.parse(data);
        isJSON = true;
    }
    catch (e) {
        isJSON = false;
    }

    if (isJSON) {
        // data is already parsed, so just use it
    }
    else {
        // try treating it as XML
    }
})