In order to load some geojson data, I need to source scripts on an external domain, say http://www.stat.ucla.edu/~jeroen/files/la_county_simplified.min.json. I have no control over the contents of this script; all I know is the url, and the name of an object defined in the script that I am interested in. A dummy version of the script looks like:
var my_data = {"foo" : 123, "bar" : 456}
Now in my application, I would like to load the my_data object dynamically from its URL. Because it is cross domain, I can't use ajax. It isn't quite jsonp either, because my script defines an object, not a function. One way would be to insert it simply as a <script> in the head of the current document. However, I would like to avoid possible side effects.
What would be a cleaner solution? I was thinking of creating an <iframe> and then inserting the <script> tag in the iframe, and extracting the object once the iframe has loaded. However I am not sure this is a reliable method that will work cross browsers (especially binding a callback to extract the object after the script has been loaded in the iframe).
Is there some library or standard solution to load a script in a clean page, and extract copy over a particular object to the main page? I already have a dependency on jQuery so that would be fine.
If you plan to do this pure client-side and can't format your data, you could use JSONP with a twist. Instead of modifying the data to fit the callback, we refit the loader to adopt to the data.
We listen for the onload of the script. When the script loads, the variable should now be in the global scope and we execute our callback, which passes that global variable into our callback.
//your script loader
function loadData(url,varName,callback){
var script = document.createElement('script');
document.getElementsByTagName('head')[0].appendChild(script);
//when the script loads, we pass in `window.my_data`
script.onload = function(){
callback.call(this,window[varName]);
};
script.src = url;
}
//using it
loadData('http://example.com/somefile.js','my_data',function(data){
//executes when script is loaded, where data is `my_data`
});
The drawback of this approach is that every time you are loading the script, you are loading it into the global scope, and collisions could happen.
There is no other way around it since you have to beat the same origin policy you have to load the script in a new script tag, JSONP works this way too but jquery hides it for you.
Either that or the site has cors headers, if the site has no cors headers here is how you can load the data (not using jsonp because it isn't in jsonp format):
function loadJS(url){
var s=document.createElement("script");
s.src=url;
$(s).on("load",function(){
console.log("var abvailable");//do something with the variable here
$(s).remove();
});
document.head.appendChild(s);
}
loadJS("http://code.jquery.com/jquery-1.9.1.min.js");
The iframe method should work fine:
create an iframe
inject a script tag that points to the file
on script load, retrieve the object
The only cross-browser issue I can think of is that you'll need to use addEventListener in modern browsers and attachEvent in old IE.
This is a standard use of an iframe as sandbox - if I understand correctly you are worried about possible conflicts with global variable names.
[Update] To address some of your comments, here is some cross-browser code:
To add an event listener:
function addEvent(element,event,fn,capture){
// capture defaults to false if omitted
if (element.addEventListener) {element.addEventListener(event,fn,(capture||false));}
// else for old IE
else {element.attachEvent('on'+event,fn);}
};
To access the iframe document:
function iframeDocument(ifr){
var doc=ifr.contentWindow||ifr.contentDocument;
if (doc.document) doc=doc.document;
return doc;
};
If you use jQuery, .on("load") and $(ifr).contents() will take care of these cross-browser compatibility issues.
JSON-P is a way of loading JavaScript from a remote domain.
The return format of the JavaScript is to invoke a function with the response data as an parameter.
someGlobalFunctionName({/* your response data */});
function someGlobalFunctionName(data) { /* do something with data */ }
Since the data is contained in an object and passed to a function, there is no global leakage other than the global function itself, which is unavoidable.
More info: http://json-p.org/
Related
From what I have read JQuery's getScript function loads the script file in a global context using a function called 'global eval'. Is there a particular setting or method to change this so it will instead load within the function I am calling it from?
If I do the following code name returns undefined as its not loading the script in the local context.
function callscript(){
var name='fred';
getScript(abc.js);
}
//abc.js:
alert(name);
I believe I have found the solution using a regular JQuery ajax call. The trick is you set the datatype to 'text' as otherwise if its script or if use getScript or the alternative .get() it will auto run the script inside and place it in the global context.
function abc(){
var msg="ciao";
$.ajax({
url: 'themes/_default/system/message.js',
success: function(data){
eval(data);
},
dataType: "text"
});
}
//message.js
(function() {
alert(msg);
})();
This alerts 'ciao' as expected :)
Before anyone says anything yes I'm using eval but its perfectly fine in this situation.
As you already noticed, there's nothing in the docs regarding this. I double checked the source code and found that the underlying call has no options for you to pass to override this behavior.
// http://code.jquery.com/jquery-1.9.1.js
...
getScript: function( url, callback ) {
return jQuery.get( url, undefined, callback, "script" );
},
...
As far as I can tell, loading a script asynchronously into a local scope is not possible with jQuery. jQuery's API doesn't give you any other means to configure its usage like this.
I am still investigating how it might be possible using some other technique.
Ok i know this is 2017, 4 years later, but it seems jQuery team never bothered to address this issue, well sort of. I had the same problem and i think this is the solution, the actual intended way of using getScript in a local context. What I noticed was that there is no way that code could be easily eval'd in a local context against your code, which jQuery has no idea how it is going. I haven't gone deeper, but if you look at the jQuery source, how it is injecting the script into the document, it's genius, it avoids eval altogether. The script it therefore ran as if it's a file that was imported through script tag. Without further ado...
I have decided to do the vice-versa of the situation, it better explains what's going on. You can then reverse it to that example in question.
If you noticed getScript actually sends a unique ID to the server in the query string. I don't know why they didn't mention this in documentation. Use that to identify returned scripts. But you have to do something in the backend...
let imports;
$.getScript("scripts.php?file=abc.js", (data, textStatus, jqXHR) => {
window[jqXHR.getResponseHeader('X-scriptID')](imports);
alert (imports.name);
});
abc.js:
imports.name = 'fred';
backend wraps whatever script we are getting scripts.php:
// code that gets the file from file system into var $output
$output = file_get_contents($_REQUEST['file']);
// generate a unique script function name, sort of a namespace
$scriptID = "__script" . $_REQUEST['_'];
// wrap the script in a function a pass the imports variable
// (remember it was defined in js before this request) we will attach
// things we want to become local on to this object in script file
$output = "window.".$scriptID."=function(imports) { ".$output." };";
// set the script id so we can find this script in js
header ("X-scriptID: " . $scriptID);
// return the output
echo $output;
What going is that the js requests a script through getScript, but it doesn't request directly to the file it uses a php script to fetch the contents of the file. I am doing this so that i can modify the returned data and attach headers that are used to id the returned script (this is large app in mind here where a lot of scripts are requested this way).
When getScript runs the returned script in the browser as usual, the actual content of the script are not ran, just a declaration of the wrapper function with a unique name __script1237863498 or something like (the number was given by getScript upon requisition of that script earlier), attached to the global window object.
Then js uses that response to run the wrapper function and inject properties into the imports object... which become local to the requesting whatever's scope.
I don't know jQuery implementation, but the reason name is returning undefined is because name is a private property of the callscript object. To negate this, you could declare the variable outside of the function call:
var name = ''; //Declare name outside of the function
function callscript(){
name='fred';
getScript('abc.js'); //Shouldn't it be $.getScript? and argument should be passed as a string
}
//abc.js:
console.log(name) //Returns undefined
callscript(); //Call the script
console.log(name); //Returns "fred"
// global.js
var global1 = "I'm a global!";
// other js-file
function testGlobal () {
alert(global1);
}
So essentially I'm trying to build my own version of GitHub's tree slider. The relevant Javascript/JQuery code is:
// handles clicking a link to move through the tree
$('#slider a').click(function() {
history.pushState({ path: this.path }, '', this.href) // change the URL in the browser using HTML5 history module
$.get(this.href, function(data) {
$('#slider').slideTo(data) // handle the page transition, preventing full page reloads
})
return false
})
// binds hitting the back button in the browser to prevent full page reloads
$(window).bind('popstate', function() {
$('#slider').slideTo(location.pathname)
}
Ok, hopefully that's understandable. Now here's my interpretation of what's going on here, followed by my problem/issue:
The callback function for the GET request when navigating through the tree is the slideTo method, and an HTML string is passed in as an argument to that function. I'm assuming that slideTo is a function defined elsewhere in the script or in a custom library, as I can't find it in the JQuery documentation. So, for my purposes, I'm trying to build my own version of this function. But the argument passed into this function, "data", is just the string of HTML returned from the GET request. However, this isn't just a snippet of HTML that I can append to a div in the document, because if I perform the same GET request (e.g. by typing the url into a web browser) I would expect to see a whole webpage and not just a piece of one.
So, within this callback function that I am defining, I would need to parse the "data" argument into a DOM so that I can extract the relevant nodes and then perform the animated transition. However, this doesn't make sense to me. It generally seems like a Bad Idea. It doesn't make sense that the client would have to parse a whole string of HTML just to access part of the DOM. GitHub claims this method is faster than a full page reload. But if my interpretation is correct, the client still has to parse a full string of HTML whether navigating through the tree by clicking (and running the callback function) or by doing full page loads such as by typing the new URL in the browser. So I'm stuck with either parsing the returned HTML string into a DOM, or ideally only fetching part of an HTML document.
Is there a way to simply load the fetched document into a Javascript or JQuery DOM object so I can easily manipulate it? or even better, is there a way to fetch only an element with an arbitrary id without doing some crazy server-side stuff (which I already tried but ended up being too spaghetti code and difficult to maintain)?
I've also already tried simply parsing the data argument into a JQuery object, but that involved a roundabout solution that only seems to work half the time, using javascript methods to strip the HTML of unwanted things, like doctype declarations and head tags:
var d = document.createElement('html');
d.innerHTML = data;
body = div.getElementsByTagName("body")[0].innerHTML;
var newDOM = $(body);
// finally I have a JQuery DOM context that I can use,
// but for some reason it doesn't always seem to work quite right
How would you approach this problem? When I write this code myself and try to make it work on my own, I feel like no matter what I do, I'm doing something horribly inefficient and hacky.
Is there a way to easily return a JQuery DOM object with a GET request? or better, just return part of a document fetched with a GET request?
Just wrap it; jQuery will parse it.
$(data) // in your callback
Imagine you want to parse a <p> tag in your normal HTML web page. You probably would use something like:
var p = $('<p>');
Right? So you have to use the same approach to parse an entire HTML document and then, navigate through the DOM tree to get the specific elements you want. Therefore, you just need to say:
$.get(this.href, function(data) {
var html = $(data);
// (...) Navigating through the DOM tree
$('#slider').slideTo( HTMLportion );
});
Notice that it also works for XML documents, so if you need to download via AJAX a XML document from the server, parse the inner information and display it on the client-side, the method is exactly the same, ok?
I hope it helps you :)
P.S: Don't ever forget to put semicolons at the end of each JavaScript sentence. Probably, if you don't put them, the engine would work but it is better to be safe and write them always!
My site uses pushState to load pages. I have one issue, I want to use javascript on one of the pages but can't because it loads everything with AJAX. So what do I do? I've been told something about "parseScript" but I can't find enough information on it.
--Example--
I load using AJAX
On my page I have this script:
<script type="text/javascript">
function go(){
alert('1');
}
</script>
GO!!!
Nothing happens.
--Edit--
If I open up Google Chrome's debugger:
"Uncaught ReferenceError: go is not defined"
And the <script> tag is no where to be found
Browsers don't seem to parse <script> element content that's added to the document via targetElement.innerHTML. That's probably what you're running into.
The best solution is to use a well-tested framework like jQuery for solving problems like this. They've already figured out how to safely and correctly inject scripts into the DOM. There's no sense re-inventing the wheel unless you absolutely can't spare the bandwidth for the library.
One way you might fix this is by separating the JavaScript from the HTML in the Ajax response, either by issuing two requests (probably slower) or by structuring your JavaScript and HTML within a JSON object (probably harder to maintain).
Here's an example:
<script>
function load_content(){
var req = new XMLHttpRequest();
req.open("GET", "ajax.json", true);
req.onreadystatechange = function (e){
if (req.readyState === 4){
if (req.status === 200){
// these three lines inject your JavaScript and
// HTML content into the DOM
var json = JSON.parse(req.responseText);
document.getElementById("target").innerHTML = json.html;
eval(json.js);
} else {
console.log("Error", req.statusText);
}
}
};
req.send(null);
}
</script>
Load more stuff
<div id="target"></div>
The document ajax.json on the server looks like this:
{
"js": "window.bar = function (){ console.log(\"bar\"); return false; }",
"html": "<p>Log a message</p>"
}
If you choose this route, you must either:
namespace your functions: MyApp.foo = function (){ ... };, or
explicitly add your functions to the global namespace: window.foo = function (){ ... };.
This is because eval executes in the current scope, so your function definitions inherit that scope and won't be globally available. In my example, I chose the latter option since it's just a trivial example, but you should be aware of why this is necessary.
Please make sure to read When is JavaScript's eval() not evil? if you decide to implement this yourself.
I think it would be helpful to have a little more detail as to how the Ajax call is made and the content is loaded. That said, a few things of note:
the syntax for javascript:void() is invalid. It should be javascript:void(0). For that matter, using javascript:void() on the href of an anchor tag is generally bad practice. Some browsers do not support it. If you must use an tag, set the href to # and add "return false;" to the click event.
you should use a button tag instead of the a tag in this case anyway.
given what you have provided, it should work (aside from the syntax error with void())
If I were to do this I would use jquery's load call.
That takes care of putting an ajax call ,and parsing tags for script/no-script elements.
IF you dont wanna use jquery, I would suggest you go online and find what the jquery load method does and implement the same as an event handler for your ajax call.
At first I made a function that received a parameter and returned jQuery such as:
function getjQuery(window)
{
/*jquery code*/(window);
return window.jQuery;
}
But then I got an email form the review and they told me I have to use jQuery file with the original file name and completely unmodified.
I started to search for an alternative and found this solution, but there is no way it work.
jQuery object is created, but I can't find any elements. $("#id").length is always 0. With the previous method it was always found.
My current code (which doesn't work)
AddonNameSpace.jQueryAux = jQuery;
AddonNameSpace.$ = function(selector,context) {
return // correct window
new AddonNameSpace.jQueryAux.fn.init(selector,context||contentWindow);
};
AddonNameSpace.$.fn =
AddonNameSpace.$.prototype = AddonNameSpace.jQueryAux.fn;
AddonNameSpace.jQuery = AddonNameSpace.$;
The jQuery file is loading on my browser.xul overlay:
<script type="text/javascript" src="chrome://addon/content/bin/jquery-1.5.2.min.js" />
Am I loading in the right place?
How can I use jQuery to modify the content on a page (HTML) with the original jQuery file, is it even possible?
You need pass the e.originalTarget.defaultView on the second parameter on jquery..
If you don't jquery will use window.document, which is the window.document from the xul.
Use
gBrowser.addEventListener("DOMContentLoaded", function (e) {
$("#id", e.originalTarget.defaultView).length
}, true);
instead of
$("#id").length;
And, for avoid conflicts with other extensions don't use script in the xul page, use MozIJSSubScriptLoader.
Components.classes["#mozilla.org/moz/jssubscript-loader;1"]
.getService(Components.interfaces.mozIJSSubScriptLoader)
.loadSubScript("chrome://youraddon/content/jquery-1.5.2.min.js");
If you use this method, you load jquery only when you need, avoiding memory leak.
The preferred way to load it is with mozIJSSubScriptLoader so you don't collide with other's extensions. I'm not sure why you're having problems, I can use jQuery in my addon like $("#id").hide() with no additional code (although from the sidebar, now browser.xul).
Either way, this blog post provides a pretty good guide and even has an example xpi to download.
I have a javascript function I'm writing which is being used to include an external JS file, but only once. The reason I need such a function is because it is being called when some content is loaded via AJAX and I need to run page-specific code to that content (no, just using .live won't cover it).
Here's my attempt, shortened for brevity:
$.include_once = function(filename) {
if ($("script[src='" + filename + "']").length === 0) {
var $node = $("<script></script>")
.attr({
src : filename,
type : "text/javascript"
})
;
$(document.body).append($node);
}
};
This works fine: the function is called, it loads the external file, and that file is being run when loaded. Perfect.
The problem is that it will always re-load that external file: the query I'm using to check for the presence of the script always finds nothing!
When debugging this, I added some lines:
alert($("script").length); // alerts: 4
$(document.body).append($node);
alert($("script").length); // alerts: 4
Looking in the dynamic source (the HTML tab of Firebug), I can't find the script tag at all.
I know that I could maintain an array of files that I've previously included, but I was hoping to go with a method such as this, which (if it worked), seems a bit more robust, since not all the JS files are being included in this way.
Can anyone explain the behaviour seen in this second snippet?
jQuery is a bit of a dumb-dumb in this case; it doesn't do at all what you'd expect. When you append($node) jQuery does this:
jQuery.ajax({
url: $node.src,
async: false,
dataType: "script"
})
Woops! For local files (eg on the same domain) jQuery performs a standard XMLHttpRequest for the .js file body, and proceeds to "eval" it by a whole convoluted process of creating a <script> tag (again!) and settings it's contents to your .js file body. This is to simulate eval but in the global context.
For cross-domain files, since it cannot perform the standard XMLHttpRequest due to the same-domain policy, jQuery once again creates a <script> element and inserts it into <head>.
In both the local and cross-domain cases above jQuery finally gets around to doing this:
head.removeChild(script);
And booms your .length check! Bummer.
So on to your problem, don't bother jQuery with this. Just do
document.getElementsByTagName('head')[0]
.appendChild(
document.createElement('script')
)
.src = filename;
Which will do what you'd expect, particularly wrt querying for it later.
You're trying to solve a problem that has already been solved several times over. Try LazyLoad for example. There are also similar plugins for jQuery.
Instead of setting the source attribute of the script-tag, set the "text" attribute of the script tag. This works in all modern browsers (the application where I use that in practice does not support IE6, so I do not know about this creep...).
In practice it would look like this (you HAVE TO add code to omit double inclusion on yourself - e.g. a simple array of all alread loaded scripts, though thats very application specific, and why should you anyway load code twice? try to omit double-loading code...!):
var script_source_code_string = <some dynamically loaded script source code>;
var $n = $("<script></script>");
$n.get(0).text = script_source_code_string;
$(document.body).append($n);
Or even simpler (without jquery, my code at this stage does not know jquery, it may also be loaded dynamically):
var script_source_code_string = <some dynamically loaded script source code>;
var s = document.createElement('script');
document.getElementsByTagName('head')[0].appendChild(s);
s.text = script_source_code_string;