I need to handle globally ajax responses. Everything works ok, out of the box, when I only want to call normal javascript action without any arguments. Than I can use p:ajaxStatus controll, and application behaves in a correct way.
What I actually now need to do, is to handle situation, when during ajax request there was externalContext.redirect() call. It happens only in one place in application, but it is called from many places.
I was thinking, that I can for instance add callback param in RequestContext. But how can I access this param in javascript?
While watching in firebug, I can see that callbackParam is returned in json response, but how can I access this value in javascript?
It's been added as a property of default args object which is available in oncomplete context.
So, for example
RequestContext.getCurrentInstance().addCallbackParam("foo", "bar");
is available as
oncomplete="console.log(args.foo)"
See also:
PrimeFaces RequestContext showcase
Update: as per the comments, that turns out to fail in <p:ajaxStatus>. I sugges to report it as a bug to PF guys, that the arguments are not available in <p:ajaxStatus oncomplete>. In the meanwhile, you can workaround it with the following script which is loaded by <h:outputScript target="head"> inside the <h:body> (to guarantee that it's loaded after PrimeFaces script):
var originalPrimeFacesAjaxUtilsSend = PrimeFaces.ajax.AjaxUtils.send;
PrimeFaces.ajax.AjaxUtils.send = function(cfg) {
var originalOncomplete = cfg.oncomplete;
cfg.oncomplete = function() {
ajaxStatusOncomplete.apply(this, arguments);
if (originalOncomplete) {
originalOncomplete.apply(this, arguments);
}
};
originalPrimeFacesAjaxUtilsSend.apply(this, arguments);
};
function ajaxStatusOncomplete(xhr, status, args) {
// Do your thing here.
}
In p:ajaxStatus params available via PrimeFaces.ajax.Queue.xhrs
For example:
oncomplete="console.log(PrimeFaces.ajax.Queue.xhrs[0].pArgs.foo)"
I have written some widgets using the jquery widget factory. Normally, I pass options and callback references using the widget constructor in a JavaScript code block.
Now I want to use the widgets in auto generated html pages and pass options to them without using JavaScript blocks. I am specifying the options in embedded json which a common JavaScript code block parses and passes it on to the widget.
<div id="search_widget">
<script type="application/json">
{
"search": {
"search_string": "text to be searched",
"callback": "a function object in an outer scope"
}
}
</script>
</div>
How do I pass the function objects preserving their scope to the widgets in json format ?
The widget will then call the function specified when a condition is met.
Thanks for your help.
You can pass the function body as text, but your receiving context will have to know it's a function and "reconstitute" it with the Function constructor (or something). You can't preserve the "scope", though that doesn't really mean much in a block of JSON.
You could also pass the function name, or some identifying pattern, or anything else you like, but all on the condition that the receiving code knows how to act on that.
JSON provides no mechanism for representing a "function". The concept is completely alien to the format, and rightly so, as it's intended to be language-neutral.
edit — Note that if you encode your function by name:
<script type="application/json">
{
"search": {
"search_string": "text to be searched",
"callback": "search_callback_23"
}
}
</script>
Then the code that grabs the object and interprets the contents can always invoke the function with the outer JSON object as the context:
function handleJSON( the_JSON_from_the_example ) {
var json = JSON.parse(the_JSON_from_the_example);
if ("search" in json) {
var searchTerm = json.search.search_string;
var callback = findCallbackFunction(json.search.callback); // whatever
callback.call(json, searchTerm); // or json.search maybe?
}
}
In other words, if the code that's interpreting the JSON-encoded information knows enough to find callback function references, then it can probably figure out an appropriate object to use as this when it calls the function.
I am just starting to get into JavaScript and couldn't find an exact scenario like this yet on SO, so I'm going to try my luck. I have two functions in an external JS file which create video feeds on our website:
function getVideos() {
//gets a list of videos
}
//callback function automatically called by getVideos()
function response(jsonData) { //can't change this line
var resp = document.getElementById("resp"); //can change this line and any subsequent lines
//parses data and populates resp
}
Then, from the HTML side, we just call getVideos() and the video feed will be created and populated.
However, I want to be able to pass any element ID I want into response() so that we can create multiple video feeds in different places on the same page. The thing is I can't change the function declaration of response() to include another parameter. Or at least I'm not led to believe I can by the company hosting our videos.
I've tried wrapping response() with getVideos() and passing an element ID from there, but then response() doesn't get called, and the only solution I can think of is resorting to storing an element ID in a global variable, which I know is a no-no in general in JavaScript.
My question is: Do I just bite the bullet and use a global variable, or is there another way?
For more info, here is our JS code as it stands now (with the closure): http://www.thebearrocks.com/Other/js/videoFeed/createVideoFeed.js
And here is the tutorial on response() we're following from the host of our videos: http://support.brightcove.com/en/video-cloud/docs/making-media-api-calls-dynamic-script-tags
may be you can use arguments? like so:
function response(jsonData) { //callback function automatically called by getVideos()
var elemId = arguments.length<2 ? "resp" : arguments[1]+"";
var resp = document.getElementById(elemId);
//parses data and populates resp
}
or, declare second argument what has default value like this:
function response(jsonData, elemId) {
elemId = elemId || "resp";
var resp = document.getElementById(elemId);
//parses data and populates resp
}
in this case function can be called as with one or two arguments
I've tried wrapping response() with getVideos() and passing an element ID from there, but then response() doesn't get called, and the only solution I can think of is resorting to storing an element ID in a global variable, which I know is a no-no in general in JavaScript.
My question is: Do I just bite the bullet and use a global variable, or is there another way?
No. Not the id variable needs to become global, but your local response function needs to for getting called back from the JSONP script - you're going to create a closure.
You can "export" it by calling
window.response = mylocalResponseFunction; // you did name that local var "response"
I'm not using eval, and I'm not sure what the problem is that Crockford has with the following. Is there a better approach to solve the following problem or is this just something I need to ignore (I prefer to perfect/improve my solutions if there is areas for improvement).
I'm using some pixel tracking stuff and in this case a client has bound a JS function to the onclick property of an HTML image tag which redirects off the site. I need to track the clicks reliably without running into race conditions with multiples of event listeners on the image. The strategy is to override the event at run time, copying and running it in my own function. Note this is being applied to a site I do not control and cannot change. So the solution looks something like:
...
func = Function(img.attr('onclick'));
...
img.attr('onclick', '');
... //some custom tracking code
func.call(this);
and the JSLint checker throws the eval is evil error.
Is there a better way to avoid race conditions for multiple events around href actions?
You're implicitly using eval because you're asking for the callback function as it was specified as an attribute in the HTML as a string and then constructing a Function with it.
Just use the img.onclick property instead, and you will directly obtain the function that the browser built from the attribute that you can then .call:
var func = img.onclick; // access already compiled function
img.onclick = null; // property change updates the attribute too
... // some custom tracking code
func.call(img, ev); // call the original function
or better yet:
(function(el) {
var old = el.onclick;
el.onclick = function() {
// do my stuff
..
// invoke the old handler with the same parameters
old.apply(this, arguments);
}
})(img);
The advantage of this latter method are two fold:
it creates no new global variables - everything is hidden inside the anonymous closure
It ensures that the original handler is called with the exact same parameters as are supplied to your replacement function
var oldClick = myImg.onclick;
myImg.onclick = function(evt){
// Put you own code here
return oldClick.call( this, evt );
};
I want to make an ajax call that will return a json object. One of this JSON object's properties will be the string of a function to be executed in the client. I realise this can easily be solved by using eval, but seeing the many disadvantages of eval, I'd rather avoid it. My question is:
Can I in some way return from the server some js code and execute it without resorting to eval?
As requested, here's some example code:
Server (Node.js):
var testFunc = function() {
alert('h1');
};
app.get('/testPack', function(req, res) {
var template = jade.render('h1 hi');
res.send({
template : template,
entity : testFunc.toString(),
data : {
id: "OMG I love this"
}
});
});
Client:
$(document).ready(function() {
$.ajax({
url: '/testPack',
success: function(data) {
$('body').append($(data.template))
alert(data.data.id);
var entity = eval(data.entity);
entity();
}
})
})
Of course, the returned function called entity wouldn't do such a silly thing, it would expose an API of the returned widget.
Just to clarify, I'd like to avoid having to make a separate call for the javascript itself. I'd rather bundle it with the template and data to render.
Easiest way to do that, is not to call a server through an ajax, but instead to create a new script tag on the page with the url pointing to a RESTful web-service that would output pure JavaScript (not JSON). That way your output will be evaluated by the browser directly without the use of eval.
To expand a little on my answer:
To get around the problems of running script in the global context you could do some tricks. For example, when you are adding script tag to the head, you can bind onload event (or rather fake onload event, since IE doesn't support onload on the script tag) to it, and if your response from the server will be always wrapped in the the function with a known name, you could apply that function from within your object. Example code below (this is just an example though):
function test ()
{
this.init = function ()
{
var script = document.createElement("script");
script.type = "text/javascript";
script.language = "javascript";
script.src = "test.js";
var me = this;
window.callMe = function () { me.scriptReady(me); };
var head = document.getElementsByTagName("head")[0];
head.appendChild(script);
};
this.scriptReady = function (object)
{
serverResponse.call(object);
};
this.name = "From inside the object";
this.init();
}
var t=new test();
The server response should look something like this:
function serverResponse()
{
alert(this.name);
}
window.callMe();
In this case, everything inside serverResponse() will use your object as "this". Now if you modify your server response in this way:
function serverResponse()
{
this.serverJSONString = { "testVar1": "1", "testVar2": 2 };
function Test()
{
alert("From the server");
}
Test();
}
window.callMe();
You can have multiple things being returned from the server and with just one response. If you don't like just setting variables, then create a function in your main object to handle JSON string that you can supply by calling this function from your response.
As you can see, it's all doable, it really doesn't look pretty, but then again, what you are trying to do is not pretty to begin with.
P.S. Just inserting a string inside tag will not work for IE, it will not allow you to do that. If you don't have to support IE, then you could get away with just inserting server response inside a newly created script tag and be done with it.
P.P.S. Please don't use this code as is, cause I didn't spend too much time writting it. It's ugly as hell, but was just ment as an example:-)
No, you can't do this by definition, because JavaScript functions are not valid JSON. See the spec here:
http://www.json.org/
If you're returning a string, then that's what it is: just a string. You can't evaluate it without eval. You can call whatever else you're returning whatever you want, but please don't call it JSON.
Here's an example of how I think this could work.
The json object represents what is returned from the server. The c and d properties contain function names as strings. If those functions are properties of some other object which exists in your page, then you should be able to call them using the object["property"] accessor.
See it working on jsFiddle: http://jsfiddle.net/WUY4n/1/
// This function is a child of the window object
window.winScopedFunction = function() {
alert("ROCK THE WIN");
}
// This function is a child of another object
var myObject = {
myFunction : function() {
alert("ROCK ON");
}
};
// pretend that this json object was the result of an ajax call.
var jsonResultFromServer= {
a : 1,
b : 2,
c : "myFunction",
d : "winScopedFunction"
};
// you can call the local functions like so
myObject[jsonResultFromServer.c]();
window[jsonResultFromServer.d]();
Yes, there's a way, but it has the exact same disadvantages as eval.
You can use the Function constructor to create a new function, and then call it. For example:
new Function(code)();
http://code.google.com/p/json-sans-eval/ is a fast JSON parser that does not use eval, and JSON.parse is becoming increasing widely available in new browsers. Both are excellent alternatives to eval for parsing JSON.
You can use the trick that Google does with Google Charts.
<html>
<head>
<script>
function onWorkDone(data) {
console.log(data);
}
</script>
<script src="callback.js"></script>
</head>
</html>
Then your callback.js is:
function doWork(callback) {
callback({result: 'foo'});
}
doWork(onWorkDone);
Basically, your script will call onWorkDone when the doWork completed. You can see a working example here:
http://jsfiddle.net/ea9Gc/
Do you have some example cases? Some things I can think of is you that you can just have a regular function inside your js file, and your server will return some parameters for your function to execute. You can even specify what function to use! (Isn't that amazing?)
// your js file
var some_namespace = {
some_function : function(a, b){
// stuff
}
}
// your server output
{
some_other_data: "123",
execute: {
func: "some_namespace.some_function",
params: [1, 2]
}
}
// your ajax callback
function(r){
window[r.execute.func].apply(this, r.execute.params);
}
The reasons of not using eval
Well, you already said it yourself. Don't use eval. But you have a wrong picture regarding why.
It is not that eval is evil. You are getting the reason wrong. Performance considerations aside, using eval this way allows a sloppy programmer to execute code passed from server on the client. Notice the "passed from server" part.
Why never execute code passed from server
Why don't you want to execute code passed from the server (incidentally that's what you're planning to do)?
When a browser executes a script on a web page, as long as the web site is valid -- i.e. really yours, and not a malware site pretending to be yours trying to trick your users -- you can be reasonably sure that every bit of code the browser is running is written by yourself.
Hacker's heaven -- script injection attacks
Now, if you are passing data from the server to your web application, and that data contains executable functions, you're asking for trouble. In the long, twisted journey of that data going from your server to your client's browser, it goes through the wild west called the Internet, perhaps through multiple layers of proxies and filters and converters, most of which you do not control.
Now, if a hacker is hiding somewhere in the middle, takes your data from the server, modify the code to those functions to something really bad, and sends it away to your client, then your client browser takes the data and executes the code. Voila! Bad things happen. The worse is: you (at the server side) will never know that your clients are hacked.
This is called a "script injection attack" and is a serious sercurity risk.
Therefore, the rule is: Never execute functions returned from a server.
Only pass data from server
If you only accept data from a server, the most that can happen whan a hacker tempers with it is that your client will see strange data coming back, and hopefully your scripts will filter them out or handle them as incorrect data. Your client's browser will not be running any arbitrary code written by the hacker with glee.
In your client-side script, of course you're sticking to the Golden Rule: Do not trust ANY data coming through the Internet. Therefore you'd already be type-check and validating the JSON data before using it, and disallowing anything that looks suspicious.
Don't do it -- pass functions from server and execute on client
So, to make a long story short: DON'T DO IT.
Think of another way to specify pluggable functionalities on the browser -- there are multiple methods.
I've had this same question, and I fixed it this way:
File: functions.js.php?f=1,3
$functions=array(
'showMessage' => 'function(msg){ alert(msg); }',
'confirmAction' => 'function(action){
return confirm("Are you sure you want to "+action+"?");
}',
'getName' => 'function getName(){
return prompt("What is your name?");
}'
);
$queried = explode($_REQUEST['f']);
echo 'var FuncUtils = {'; // begin javascript object
$counter=1;
foreach($functions as $name=>$function){
if(in_array($counter, $queried))
echo '"'.$name.'":,'.$function.',';
$counter++;
}
echo '"dummy":null };'; // end javascript object
File: data5.json
{
"action" : ['confirmAction','exit']
}
File: test.js
$(document).ready(function(){
$.getScript('functions.js.php?f=1,3');
});
function onBeforeExit(){
$.getJSON('data5.json', function(data) {
var func = data.action.shift();
FuncUtils[func].apply(null, data.action);
});
}