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Executing a script from jQuery GET request

I'm sending a GET request with jQuery
$.get("/index.html", /*Adding '?update' to the request*/ "update",
function (data) {/* Enter code here */}, "html");
where data is my server's response. I'm sending back a simple script like alert() so the 'data' variable equals <script> alert("Hello world!") </script>.
I need a way to automatically execute the script. I could just .append(data) to an element but I'm having multiple appends so that isn't really practical.
What is the easiest and the most practical way of executing the script?

Either .append it, like you said, or use eval(data), but then you'd have to get rid of the <script></script>. You can supply eval() a piece of Javascript code and it will execute that.
Please be aware that using eval should be avoided at all costs.

I did some crazy stuff in a case like this but you may think it is extreme. In my case I had to store some functions in localStorage and execute them by history state ( when user goes back/forth ). I have created a json object similar to
{obj:'myObject', fn: 'myfn', args: myArgs}
then stored this data base64 encoded. then when I need it back, I simply decoded content and
window.[data.fn].[data.obj].apply(null,data.args)`
did the trick without exposing too much data and not using eval. Eval comes from Evil so I would stay away. =)
UPDATE
So in my case all main core functions are json objects at window namespace similar to ( not actual content but an sample)
Member = {
initialize: function (){
//some process
},
render:function(memberId, selector){
//Some process
},
//...etc }
So when I store each item it, I used something similar to
var data = {obj: 'Member', fn: 'render', args: [1,'#member-block']}
then encoded version will be
localStorage.setItem('data', btoa(JSON.stringify(data)));
dmFyIGRhdGEgPSB7b2JqOiAnTWVtYmVyJywgZm46ICdyZW5kZXInLCBhcmdzOiB7bWVtYmVySWQ6MSwgc2VsZWN0b3I6ICcjbWVtYmVyLWJsb2NrJ319
Then when I need to call back
var data = JSON.parse(atob(localStorage.getItem('data'));
would return my original data object. Since the main functions in my case are in window namespace.
if (typeof window[data.obj]!=='undefined') { // same as window.Member
if (typeof window[data.obj][data.fn]!=='undefined' && typeof window[data.obj][data.fn]!=='function' ) { // make sure fn is defined and is a function
window[data.obj][data.fn].apply(null, data.args);
// we pass same arguments to function call with apply.
// `apply` will give us option to add arguments dynamically without knowing its size.
// it can be null any number of arguments that needed for that function.
}
}

Loading Custom Component ViewModel from JavaScript file

I'm trying to create a custom component loader within knockout but I'm struggling with the view model. Essentially I want to remotely go grab both the HTML template and the JavaScript view model, but in this instance I don't want to use a traditional AMD module loader.
I've managed to get some of this working, specifically loading the HTML template but I can't figure out how to load the view model. Before I start here's my directory structure:
-- index.html
-- customerLoader.js
-- comps
   -- myCustom.html
   -- myCustom.js
So I've created my component loader like so. getConfig basically takes the name of the component and turns that into a path for the viewModel and the html template.
var customLoader = {
getConfig: function(name, callback) {
callback({ template: "comps/" + name + ".html", viewModel: "comps/" + name + ".js" });
},
loadTemplate: function(name, templateConfig, callback) {
console.log("loadTemplate", name, templateConfig);
$.get(templateConfig, function(data) {
callback(data);
});
},
loadViewModel: function(name, templateConfig, callback) {
console.log("loadViewModel", name, templateConfig);
$.getScript(templateConfig, function(data) {
callback(data);
});
}
};
ko.components.loaders.unshift(customLoader);
This successfully makes a request to load the template, which brings back some basic content. What I'm struggling with is the view model. I'm not sure what should be in the target of my JavaScript file?
I assumed that I'd want to return a function that would take some parameters, most likely a params object. However if I try and do this I get an error, telling me the JavaScript is invalid:
Uncaught SyntaxError: Illegal return statement
This is the current content I've got that is producing this error:
return function(params) {
console.log("myCustom.js", name, viewModelConfig);
// Add a computed value on
params.bookNum = ko.computed(function() {
switch(this.title()) {
case "A": return 1;
case "B": return 2;
case "C": return 3;
default: return -1;
}
});
//ko.components.defaultLoader.loadViewModel(name, viewModelConstructor, callback);
};
So ultimately I'm not sure how to achieve this, but I guess there are 3 basic questions that explain the gaps in my understanding:
What should my "view model" JavaScript file contain exactly? A function? An object? etc...
Do I need to call the ko.components.defaultLoader.loadViewModel at all?
Within my customLoader what should loadViewModel() be doing with the result of the jQuery callback? I'm not sure if I get back a JavaScript object, or just a string?
I'm open to achieve this in a different way if need be (e.g. not using jQuery but getting files a different way), but I don't want to use a module loader (e.g. require.js/curl.js in this instance).

First lets figure out what is happening...
From the docs:
This ($.getScript()) is a shorthand Ajax function, which is equivalent to:
$.ajax({
url: url,
dataType: "script",
success: success
});
And from jQuery.ajax():
...
dataType: ...
"script": Evaluates the response as JavaScript and returns it as plain text.
So your code is fetched, evaluated and then would have been returned as text, but evaluation first fails because you can't return if you're not within a function.
So what can be done? There are several options:
Use a module loader.
jQuery isn't a module loader, and as such it doesn't have the ability to parse fetched code and create a value / object from that code. A module loader is designed specifically for this task. It will take a script written in a specific pattern and "evaluate" it into a value (typically an object with 1 or more properties).
Change your script to a legal script
Because it's illegal to have a return statement in global code, your current code fails. You could however create a named function (or a variable with a function expression) and then use that name to reference that function. It could look like this:
function myCreateViewModel(param) {
// whatever
}
And the usage would be:
$.getScript(templateConfig, function() {
callback(myCreateViewModel);
});
The downside here is that if you ever go through that code path twice in the same page, your script will overwrite the old declaration. That might not ever be a problem, but it feels dirty.
Not use $.getScript(), use $.ajax() (or $.get()) with dataType: 'text' and evaluate yourself.
Remove the return from your code, and wrap it with an eval(). It will be evaluated as a function expression, the return value of the eval will be your function, and you could pass that directly to the callback:
$.get({
url: templateConfig,
dataType: 'text',
success: function(text) {
callback(eval(text));
}
});
This will work, but it will use the frowned upon eval(), which is exposing you to various risks.

How to reach JSON data inside parenthesis

I have a JSON response like this:
google.friendconnect.container["renderOpenSocialGadget"](
{
height: 200,
url: "http://username.github.io/",
"view-params": {"style":"light","url":"https://www.facebook.com/username","height":"258"},
"prefs": {"style":"light","url":"https://www.facebook.com/username","height":"258"}
}, skin);
I want to reach the values such as height, url, view-params but couldn't.
I tried this but it didn't worked:
console.log(google.friendconnect.container["renderOpenSocialGadget"].url);

The expression google.friendconnect.container["renderOpenSocialGadget"]( is equivalent to google.friendconnect.container.renderOpenSocialGadget(
Given that, we see that this is a method of an object, getting a JSON object and an additional parameter (skin) as parameters.
As the object is somehow "anonymous" parsed directly in to the function call, you can't access it anymore, once the function has consumed it.
Check, if google.friendconnect.container has getter methods (they usually have ...) by console.log(google.friendconnect.container).
EDIT
Just an Idea: you might catch the call and pass it over:
google.friendconnect.container["MyrenderOpenSocialGadget"] =
google.friendconnect.container["renderOpenSocialGadget"];
google.friendconnect.container["renderOpenSocialGadget"] = function(obj, skin) {
// do what you want with obj
console.log(obj.url);
//call original
google.friendconnect.container["MyrenderOpenSocialGadget"](obj, skin);
});

How do I pass the name of a function as a parameter then reference that function later?

I want to pass the name of a function "testMath" as a string into a wrapper function called "runTest" as a parameter. Then inside 'runTest' I would call the function that was passed. The reason I'm doing this is because we have a set of generic data that will populate into variables regardless of the test, then a specific test can be called, based on whatever the user wants to test. I am trying to do this using javascript/jquery. In reality the function is much more complex including some ajax calls, but this scenario highlights the basic challenge.
//This is the wrapper that will trigger all the tests to be ran
function performMytests(){
runTest("testMath"); //This is the area that I'm not sure is possible
runTest("someOtherTestFunction");
runTest("someOtherTestFunctionA");
runTest("someOtherTestFunctionB");
}
//This is the reusable function that will load generic data and call the function
function runTest(myFunction){
var testQuery = "ABC";
var testResult = "EFG";
myFunction(testQuery, testResult); //This is the area that I'm not sure is possible
}
//each project will have unique tests that they can configure using the standardized data
function testMath(strTestA, strTestB){
//perform some test
}

Do you need the function names as string? If not, you can just pass the function like this:
runTheTest(yourFunction);
function runTheTest(f)
{
f();
}
Otherwise, you can call
window[f]();
This works, because everything in the 'global' scope is actually part of the window object.

Inside runTests, use something like this:
window[functionName]();
Make sure testMath in the global scope, though.

I preffer to use apply/call approach when passing params:
...
myFunction.call(this, testQuery, testResult);
...
More info here.

Avoiding eval when executing js returned from ajax call

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);
});
}