How to check if ajax response is javascript content type?

Question

I have several different forms that each return something different. I need to detect if it's a simple string (so i can put it in the error/status area) or if its javascript I do nothing and let it execute.

This is currently how I'm doing my checking, but I want to make sure this is 100% sturdy and reliable... I couldn't think of any other way.

The other option would be to always use JSON, but then I need a JSON shim, as well as somehow trying to serialize javascript into JSON.

  $.ajax({
    type: 'POST',
    url:  form.attr('action'),
    data: form.serialize()
  })
  .done(function(data, textStatus, xhr) {
    if (!xhr.getResponseHeader('Content-Type').match(/text\/javascript/i)) {
      form.find('.status').text(data).removeClass().addClass('status status-done').slideDown(200);
    } else { 
      // this is where i do nothing and let JS run
    }
  })

The following works, but I'm afraid there would be some edge case where it's not going to work (not sure what that might be, but it's important this section works 100%)

Why do you need a JSON shim? What ancient browsers you need to support? I think you're facing an XY problem here... — elclanrs
– elclanrs, Commented Aug 30, 2014 at 23:32
I'd recommend that you read up on ajax dataType's as it appears that you got some bad information. api.jquery.com/jquery.ajax — Bob Tate
– Bob Tate, Commented Aug 30, 2014 at 23:38
How should I differentiate between JSON and application/javascript then? — Tallboy
– Tallboy, Commented Aug 30, 2014 at 23:53
@Tallboy The server/application should be responding with Content-Type: application/json or at least similar for JSON. (Unless it's JSON-P.) — Jonathan Lonowski
– Jonathan Lonowski, Commented Aug 30, 2014 at 23:55
I know that, but my question revolves around... what is the best way to have my .done() ajax promise determine if the response is application/json (show the error message above the form), or... application/javascript (do nothing and let the JS execute. i dont want to be injecting the response JS into the form so i need to determine the content type) — Tallboy
– Tallboy, Commented Aug 30, 2014 at 23:58

Community · Accepted Answer · 2017-05-23 12:21:39Z

Note, Not certain about detail of requirement . If interpret Question correctly , at different form elements , different response types from $.ajax() requests ? a) Check for response type string ? b) do nothing ?

Could possibly check for response type string within json response with

if (typeof data.data === "string") { 
  // do stuff , with `string`
}

if $.ajax() expect json response , receive js , could possible run the piece immediately. At piece below , first response is string , filtered through if at .done() . Second response json object having a js function expression as property , which appear to run immediately , at $.ajax() success textStatus . Still capable to check response type of object at else , though , run as script . See empty xhr.repsonseText and xhr.reponseJSON at console

Try

var urls = [["/echo/json/","abc"]
            , ["/echo/json/",
              {"abc": 
                (function() { 
                    setTimeout(function() {
                        $("body").append("<div id=data>" 
                        + "object" + "</div>"); 
                        $("#data")
                        .hide(0)
                        .fadeIn(1200)},1200) 
                 }())
               }]
            ];


    var request = function(url, _data) {
    $.ajax({
        type: 'POST',
        url:  url,
        data: {json : JSON.stringify({"data":_data})}
      })
      .done(function(data, textStatus, xhr) {
        if (typeof data.data === "string") {
            $("body").append("<div>" + data.data + "</div>")
        } else { 
            console.log(typeof data.data
                        , data
                        , xhr.responseText
                        , xhr.responseJSON);
          // this is where i do nothing and let JS run
        }
      })
    };

    $.each(urls, function(k, v) {
      request(v[0], v[1])
    });

jsfiddle http://jsfiddle.net/guest271314/y9b7t740/

See

jQuery getScript() vs document.createElement('script') , script.js

Calling a JavaScript function returned from an Ajax response

jQuery: Evaluate script in ajax response

What is JSONP all about?

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