I have some crazy app done almost 100% by manipulating the DOM and I find myself in the unfortunate position of changing something in it. As there are probably around 100 different scripts that do God knows what, I have no clue in which file should I look to make my changes. So, I want to ask, is there a way (using Firebug maybe or something similar) to know where a specific piece of html was generated? I'm a C developer, so I'm not very good at this, it drives me crazy.
Are all the elements added at the page load, or partially in the response to the user input? (clicking etc.)
for stuff added with the response to your actions, you can use Firebug's "Break On Next" button in the "Script" tab. To active BON you have to click it, or, in just-shipped Firebug 1.10.0a8, use keyboard shortcut ALT-CTRL-B (useful when you have event listeners bound to mouse movements). Then, when any piece of JS is going to be executed in reaction to your click etc., you will hit a breakpoint.
for stuff added at page load time, you may use the trick of extending the native functions (this might sound crazy - yeah it is, don't do it in production!) like appendChild, insertBefore, replaceChild. Just insert the appropriate code at the very top of your main HTML file, so all the code below will "see" the change.
Unfortunately, this does not work in Firefox due to a bug. But works in Opera and I guess in Chrome as well.
When you extend the native function, you can inject any code before really adding the node to the page. For instance, call console.log or create a breakpoint, to inspect the current page state. You can try playing with breakpoints to see the available variables properties inside those function to adjust what you push to console.log.
For this code:
<!doctype html>
<html>
<head>
<script type="text/javascript">
// this should work in Firefox but it does not -- https://bugzilla.mozilla.org/show_bug.cgi?id=618379
// works at least in Opera, probably Chrome too
Node.prototype._appendChild = Node.prototype.appendChild;
Node.prototype.appendChild = function(child) {
console.log("appending " + child + " to " + this);
return this._appendChild(child); // call the original function with the original parameters
}
// this works in Firefox
document._createElement = document.createElement;
document.createElement = function(tagName){
console.log("creating " + tagName);
return this._createElement(tagName);
}
</script>
</head>
<body>
<script type="text/javascript">
var p = document.createElement("p");
p.appendChild( document.createTextNode("abc"));
document.body.appendChild(p);
</script>
</body>
</html>
Opera outputs:
creating p appendChild.html:14
appending [object Text] to [object HTMLParagraphElement] appendChild.html:7
appending [object HTMLParagraphElement] to [object HTMLBodyElement] appendChild.html:7
To overcome the weakness of Firefox (that you can't override appendChild), you may use the trick: place the code below instead in the top of your HTML
<script>
Node.prototype._appendChild = function(child) {
console.log("appending " + child + " to " + this);
return this.appendChild(child)
};
</script>
and then, use Fiddler proxy by creating auto-responders (WMV tutorial, 9.9 MB) where you manually replace all calls to .appendChild with ._appendChild (you can use Notepad++ for "find replace in all opened files"). Creating auto-responders and hand-tampering requests can be mundane, but it's extremely powerful. To quickly create auto-responder rule, load the page when Fiddler is active, then drag'n'drop files as in the picture below. For each file, right click and choose "Generate File" from menu (this will put a file on the desktop) or create a file by yourself in different location. (it's good to open Fiddler-generated files and remove response headers from them; BTW "Generate file" puts real contents only if the response header was 200, so make sure to load the page with CTRL-F5 to skip the cache).
In Chrome you can inspect an element and right click on it. This menu gives you some options to break when something below the element is changed or when it's own attributes change. Maybe one of those breakpoints will find what you are looking for?
Assuming you've got access to the raw (hopefully un-minified/obfuscated) JS files, maybe just search them for text strings related to DOM manipulation and/or attributes of the node you're trying to find the creation of? I'd try things like "appendChild" "createElement" and the node's ID/class names.
You could also set break points all over the script files, and step through them as the page loads to help you narrow down where to look. Might help to start by just "pausing" the JS execution and stepping through from the very beginning.
If you can share the code (a link to the live site would do fine) I'd be happy to take a look.
If you are using the jQuery framework in your javascript to make the DOM changes then you may find the fireQuery plugin for FireBug in the firefox browser may get you the information you need.
Example:
It adds additional information to the standard HTML view by superimposing additional jquery element information to the display to provide a deeper insight into how your javascript is amending the page content.
I hope that helps you out.
Related
In tutorials I've learnt to use document.write. Now I understand that by many this is frowned upon. I've tried print(), but then it literally sends it to the printer.
So what are alternatives I should use, and why shouldn't I use document.write? Both w3schools and MDN use document.write.
The reason that your HTML is replaced is because of an evil JavaScript function: document.write().
It is most definitely "bad form." It only works with webpages if you use it on the page load; and if you use it during runtime, it will replace your entire document with the input. And if you're applying it as strict XHTML structure it's not even valid code.
the problem:
document.write writes to the document stream. Calling document.write on a closed (or loaded) document automatically calls document.open which will clear the document.
-- quote from the MDN
document.write() has two henchmen, document.open(), and document.close(). When the HTML document is loading, the document is "open". When the document has finished loading, the document has "closed". Using document.write() at this point will erase your entire (closed) HTML document and replace it with a new (open) document. This means your webpage has erased itself and started writing a new page - from scratch.
I believe document.write() causes the browser to have a performance decrease as well (correct me if I am wrong).
an example:
This example writes output to the HTML document after the page has loaded. Watch document.write()'s evil powers clear the entire document when you press the "exterminate" button:
I am an ordinary HTML page. I am innocent, and purely for informational purposes. Please do not <input type="button" onclick="document.write('This HTML page has been succesfully exterminated.')" value="exterminate"/>
me!
the alternatives:
.innerHTML This is a wonderful alternative, but this attribute has to be attached to the element where you want to put the text.
Example: document.getElementById('output1').innerHTML = 'Some text!';
.createTextNode() is the alternative recommended by the W3C.
Example: var para = document.createElement('p');
para.appendChild(document.createTextNode('Hello, '));
NOTE: This is known to have some performance decreases (slower than .innerHTML). I recommend using .innerHTML instead.
the example with the .innerHTML alternative:
I am an ordinary HTML page.
I am innocent, and purely for informational purposes.
Please do not
<input type="button" onclick="document.getElementById('output1').innerHTML = 'There was an error exterminating this page. Please replace <code>.innerHTML</code> with <code>document.write()</code> to complete extermination.';" value="exterminate"/>
me!
<p id="output1"></p>
Here is code that should replace document.write in-place:
document.write=function(s){
var scripts = document.getElementsByTagName('script');
var lastScript = scripts[scripts.length-1];
lastScript.insertAdjacentHTML("beforebegin", s);
}
You can combine insertAdjacentHTML method and document.currentScript property.
The insertAdjacentHTML() method of the Element interface parses the specified text as HTML or XML and inserts the resulting nodes into the DOM tree at a specified position:
'beforebegin': Before the element itself.
'afterbegin': Just inside the element, before its first child.
'beforeend': Just inside the element, after its last child.
'afterend': After the element itself.
The document.currentScript property returns the <script> element whose script is currently being processed. Best position will be beforebegin — new HTML will be inserted before <script> itself. To match document.write's native behavior, one would position the text afterend, but then the nodes from consecutive calls to the function aren't placed in the same order as you called them (like document.write does), but in reverse. The order in which your HTML appears is probably more important than where they're place relative to the <script> tag, hence the use of beforebegin.
document.currentScript.insertAdjacentHTML(
'beforebegin',
'This is a document.write alternative'
)
As a recommended alternative to document.write you could use DOM manipulation to directly query and add node elements to the DOM.
Just dropping a note here to say that, although using document.write is highly frowned upon due to performance concerns (synchronous DOM injection and evaluation), there is also no actual 1:1 alternative if you are using document.write to inject script tags on demand.
There are a lot of great ways to avoid having to do this (e.g. script loaders like RequireJS that manage your dependency chains) but they are more invasive and so are best used throughout the site/application.
I fail to see the problem with document.write. If you are using it before the onload event fires, as you presumably are, to build elements from structured data for instance, it is the appropriate tool to use. There is no performance advantage to using insertAdjacentHTML or explicitly adding nodes to the DOM after it has been built. I just tested it three different ways with an old script I once used to schedule incoming modem calls for a 24/7 service on a bank of 4 modems.
By the time it is finished this script creates over 3000 DOM nodes, mostly table cells. On a 7 year old PC running Firefox on Vista, this little exercise takes less than 2 seconds using document.write from a local 12kb source file and three 1px GIFs which are re-used about 2000 times. The page just pops into existence fully formed, ready to handle events.
Using insertAdjacentHTML is not a direct substitute as the browser closes tags which the script requires remain open, and takes twice as long to ultimately create a mangled page. Writing all the pieces to a string and then passing it to insertAdjacentHTML takes even longer, but at least you get the page as designed. Other options (like manually re-building the DOM one node at a time) are so ridiculous that I'm not even going there.
Sometimes document.write is the thing to use. The fact that it is one of the oldest methods in JavaScript is not a point against it, but a point in its favor - it is highly optimized code which does exactly what it was intended to do and has been doing since its inception.
It's nice to know that there are alternative post-load methods available, but it must be understood that these are intended for a different purpose entirely; namely modifying the DOM after it has been created and memory allocated to it. It is inherently more resource-intensive to use these methods if your script is intended to write the HTML from which the browser creates the DOM in the first place.
Just write it and let the browser and interpreter do the work. That's what they are there for.
PS: I just tested using an onload param in the body tag and even at this point the document is still open and document.write() functions as intended. Also, there is no perceivable performance difference between the various methods in the latest version of Firefox. Of course there is a ton of caching probably going on somewhere in the hardware/software stack, but that's the point really - let the machine do the work. It may make a difference on a cheap smartphone though. Cheers!
The question depends on what you are actually trying to do.
Usually, instead of doing document.write you can use someElement.innerHTML or better, document.createElement with an someElement.appendChild.
You can also consider using a library like jQuery and using the modification functions in there: http://api.jquery.com/category/manipulation/
This is probably the most correct, direct replacement: insertAdjacentHTML.
Try to use getElementById() or getElementsByName() to access a specific element and then to use innerHTML property:
<html>
<body>
<div id="myDiv1"></div>
<div id="myDiv2"></div>
</body>
<script type="text/javascript">
var myDiv1 = document.getElementById("myDiv1");
var myDiv2 = document.getElementById("myDiv2");
myDiv1.innerHTML = "<b>Content of 1st DIV</b>";
myDiv2.innerHTML = "<i>Content of second DIV element</i>";
</script>
</html>
Use
var documentwrite =(value, method="", display="")=>{
switch(display) {
case "block":
var x = document.createElement("p");
break;
case "inline":
var x = document.createElement("span");
break;
default:
var x = document.createElement("p");
}
var t = document.createTextNode(value);
x.appendChild(t);
if(method==""){
document.body.appendChild(x);
}
else{
document.querySelector(method).appendChild(x);
}
}
and call the function based on your requirement as below
documentwrite("My sample text"); //print value inside body
documentwrite("My sample text inside id", "#demoid", "block"); // print value inside id and display block
documentwrite("My sample text inside class", ".democlass","inline"); // print value inside class and and display inline
I'm not sure if this will work exactly, but I thought of
var docwrite = function(doc) {
document.write(doc);
};
This solved the problem with the error messages for me.
I'm trying to load a parent page into an object tag, and whilst I can get an alert to show I've got the code, I cannot get it into the <object> Any clues?
var page=parent.document.documentElement.innerHTML;
alert(page);
document.getElementById('close_skin').style.visibility="visible";
document.getElementById('show_skin').style.visibility="visible";
document.getElementById('show_skin').setAttribute("data",page);
Assuming I can get the code to appear, how can I "toggle" to a different set of styles? The parent uses ".xxx_fixed" classes, but the code in the object needs to use the ".xxx_float" classes that are also in the template CSS at top of page. (When I did it in another PERL program, it was easy just to rename the tags in the <body> from "class='xxx_fixed' " to "class='xxx_float' " (Can't do that so easily with global javascript replace as that would also rename the classes at top of code as well!)
I have just tried adding some script to the top of the var page object - which MAY work if I can get the code to appear ...
+'document.getElementById(\'icon_outer\').setAttribute(\'class\', \'icon_outer_float\')'
If you're interested as to the "why", the "fixed" keep menu / top bar fixed in one place when viewed in full screen browser, but the 'float' makes everything move in unison within the <object> "window" allowing viewer to pan around the template page like a static magnifying glass;
.menu_back_float{position:relative;top:0px;background-color:#f5eca4;min-height:520px;height:auto}
.menu_back_fixed{position:relative;top:35px;background-color:#f5eca4;min-height:550px;height:auto}
To load the parent page into an <object> element, you have to specify the URL of the page. To get the code and place it in a alert box, you can use jQuery's $.get() method (as long as you load it via a proxy domain), like this:
HTML:
// I'm just using W3Schools just to save time
<object data="http://www.w3schools.com/" width="1500" height="1200">
<embed src="http://www.w3schools.com/" width="1500" height="1200"></embed>
Your browser does not support the object tag.
</object>
JavaScript:
window.jQuery.get("http://www.yourdomain.com/?url=www.w3schools.com", function(response) {
window.alert(response);
}
For the second part of your question, you can use jQuery to change the name of the class from .xxx_fixed to .xxx_float:
function main() {
$('object').removeClass('xxx_fixed').addClass('xxx_float');
}
$(document).ready(main);
Hopefully I have answered your question correctly and thouroughly, and if I haven't, feel free to let me know so I can edit this.
I have the non-standard element
<testele></testele>
In every browser except IE, this bit of JavaScript will successfully change the content of the above element
document.getElementsByTagName("testele")[0].innerHTML = 'hi';
However, if I change the <testele> to just a <span> (in the HTML and the JavaScript), it now successfully changes the content of the element in every browser, including IE.
Is there any fix? I have searched around and tried a bunch to no avail.
Use document.createElement("testele") before it is rendered. This script must be included before the document encouters a <testele>:
http://jsfiddle.net/gilly3/LjwbA/
document.createElement("testele");
window.onload = function() {
document.getElementsByTagName("testele")[0].innerHTML = 'hi';
};
If you try to do document.createElement("testele") after a <testele> has been parsed by the browser, it's too late.
Take a look at innerShiv, a Javascript plugin which aims to solve this.
In tutorials I've learnt to use document.write. Now I understand that by many this is frowned upon. I've tried print(), but then it literally sends it to the printer.
So what are alternatives I should use, and why shouldn't I use document.write? Both w3schools and MDN use document.write.
The reason that your HTML is replaced is because of an evil JavaScript function: document.write().
It is most definitely "bad form." It only works with webpages if you use it on the page load; and if you use it during runtime, it will replace your entire document with the input. And if you're applying it as strict XHTML structure it's not even valid code.
the problem:
document.write writes to the document stream. Calling document.write on a closed (or loaded) document automatically calls document.open which will clear the document.
-- quote from the MDN
document.write() has two henchmen, document.open(), and document.close(). When the HTML document is loading, the document is "open". When the document has finished loading, the document has "closed". Using document.write() at this point will erase your entire (closed) HTML document and replace it with a new (open) document. This means your webpage has erased itself and started writing a new page - from scratch.
I believe document.write() causes the browser to have a performance decrease as well (correct me if I am wrong).
an example:
This example writes output to the HTML document after the page has loaded. Watch document.write()'s evil powers clear the entire document when you press the "exterminate" button:
I am an ordinary HTML page. I am innocent, and purely for informational purposes. Please do not <input type="button" onclick="document.write('This HTML page has been succesfully exterminated.')" value="exterminate"/>
me!
the alternatives:
.innerHTML This is a wonderful alternative, but this attribute has to be attached to the element where you want to put the text.
Example: document.getElementById('output1').innerHTML = 'Some text!';
.createTextNode() is the alternative recommended by the W3C.
Example: var para = document.createElement('p');
para.appendChild(document.createTextNode('Hello, '));
NOTE: This is known to have some performance decreases (slower than .innerHTML). I recommend using .innerHTML instead.
the example with the .innerHTML alternative:
I am an ordinary HTML page.
I am innocent, and purely for informational purposes.
Please do not
<input type="button" onclick="document.getElementById('output1').innerHTML = 'There was an error exterminating this page. Please replace <code>.innerHTML</code> with <code>document.write()</code> to complete extermination.';" value="exterminate"/>
me!
<p id="output1"></p>
Here is code that should replace document.write in-place:
document.write=function(s){
var scripts = document.getElementsByTagName('script');
var lastScript = scripts[scripts.length-1];
lastScript.insertAdjacentHTML("beforebegin", s);
}
You can combine insertAdjacentHTML method and document.currentScript property.
The insertAdjacentHTML() method of the Element interface parses the specified text as HTML or XML and inserts the resulting nodes into the DOM tree at a specified position:
'beforebegin': Before the element itself.
'afterbegin': Just inside the element, before its first child.
'beforeend': Just inside the element, after its last child.
'afterend': After the element itself.
The document.currentScript property returns the <script> element whose script is currently being processed. Best position will be beforebegin — new HTML will be inserted before <script> itself. To match document.write's native behavior, one would position the text afterend, but then the nodes from consecutive calls to the function aren't placed in the same order as you called them (like document.write does), but in reverse. The order in which your HTML appears is probably more important than where they're place relative to the <script> tag, hence the use of beforebegin.
document.currentScript.insertAdjacentHTML(
'beforebegin',
'This is a document.write alternative'
)
As a recommended alternative to document.write you could use DOM manipulation to directly query and add node elements to the DOM.
Just dropping a note here to say that, although using document.write is highly frowned upon due to performance concerns (synchronous DOM injection and evaluation), there is also no actual 1:1 alternative if you are using document.write to inject script tags on demand.
There are a lot of great ways to avoid having to do this (e.g. script loaders like RequireJS that manage your dependency chains) but they are more invasive and so are best used throughout the site/application.
I fail to see the problem with document.write. If you are using it before the onload event fires, as you presumably are, to build elements from structured data for instance, it is the appropriate tool to use. There is no performance advantage to using insertAdjacentHTML or explicitly adding nodes to the DOM after it has been built. I just tested it three different ways with an old script I once used to schedule incoming modem calls for a 24/7 service on a bank of 4 modems.
By the time it is finished this script creates over 3000 DOM nodes, mostly table cells. On a 7 year old PC running Firefox on Vista, this little exercise takes less than 2 seconds using document.write from a local 12kb source file and three 1px GIFs which are re-used about 2000 times. The page just pops into existence fully formed, ready to handle events.
Using insertAdjacentHTML is not a direct substitute as the browser closes tags which the script requires remain open, and takes twice as long to ultimately create a mangled page. Writing all the pieces to a string and then passing it to insertAdjacentHTML takes even longer, but at least you get the page as designed. Other options (like manually re-building the DOM one node at a time) are so ridiculous that I'm not even going there.
Sometimes document.write is the thing to use. The fact that it is one of the oldest methods in JavaScript is not a point against it, but a point in its favor - it is highly optimized code which does exactly what it was intended to do and has been doing since its inception.
It's nice to know that there are alternative post-load methods available, but it must be understood that these are intended for a different purpose entirely; namely modifying the DOM after it has been created and memory allocated to it. It is inherently more resource-intensive to use these methods if your script is intended to write the HTML from which the browser creates the DOM in the first place.
Just write it and let the browser and interpreter do the work. That's what they are there for.
PS: I just tested using an onload param in the body tag and even at this point the document is still open and document.write() functions as intended. Also, there is no perceivable performance difference between the various methods in the latest version of Firefox. Of course there is a ton of caching probably going on somewhere in the hardware/software stack, but that's the point really - let the machine do the work. It may make a difference on a cheap smartphone though. Cheers!
The question depends on what you are actually trying to do.
Usually, instead of doing document.write you can use someElement.innerHTML or better, document.createElement with an someElement.appendChild.
You can also consider using a library like jQuery and using the modification functions in there: http://api.jquery.com/category/manipulation/
This is probably the most correct, direct replacement: insertAdjacentHTML.
Try to use getElementById() or getElementsByName() to access a specific element and then to use innerHTML property:
<html>
<body>
<div id="myDiv1"></div>
<div id="myDiv2"></div>
</body>
<script type="text/javascript">
var myDiv1 = document.getElementById("myDiv1");
var myDiv2 = document.getElementById("myDiv2");
myDiv1.innerHTML = "<b>Content of 1st DIV</b>";
myDiv2.innerHTML = "<i>Content of second DIV element</i>";
</script>
</html>
Use
var documentwrite =(value, method="", display="")=>{
switch(display) {
case "block":
var x = document.createElement("p");
break;
case "inline":
var x = document.createElement("span");
break;
default:
var x = document.createElement("p");
}
var t = document.createTextNode(value);
x.appendChild(t);
if(method==""){
document.body.appendChild(x);
}
else{
document.querySelector(method).appendChild(x);
}
}
and call the function based on your requirement as below
documentwrite("My sample text"); //print value inside body
documentwrite("My sample text inside id", "#demoid", "block"); // print value inside id and display block
documentwrite("My sample text inside class", ".democlass","inline"); // print value inside class and and display inline
I'm not sure if this will work exactly, but I thought of
var docwrite = function(doc) {
document.write(doc);
};
This solved the problem with the error messages for me.
I'm working on some custom Javascript for a CMS template at work. I want to be able to make a certain <li> element on the page receive the class of "current" for that page only. So in the global page head I have something like this:
<script type="text/javascript">
function makeCurrent(id) {
var current = document.getElementById(id);
current.setAttribute("class", "current"); // for most browsers
current.setAttribute("className", "current"); // for ie
}
</script>
Then in each individual page <head>, I have something like this:
<script type="text/javascript">makeCurrent("undergraduate")</script>
On the page I have a nav <ul>, with something like:
<li id="undergraduate">Undergraduate Program</li>
<li id="graduate">Graduate Program</li>
etc.
When I load the page, the class is not applied. When I look in the Firebug console, it gives the error message:
current is null
(x) current.setAttribute("class", "current");
I'm still getting the hang of writing solid, raw javascript (learning backwards after jQuery, you know how it goes), but I want to write it in just JS. What idiotic newbie mistake am I making?
Thanks everyone!
If you execute the javascript before the DOM tree has finished loading, it will return null. So an idea would be to call the function all the way at the end before you close the body tag.
This is why most JavaScript libraries have support for a dom-ready event, modern browsers have this as well (domcontentloaded) however for wide browser support it's a little trickier to do it for yourself (well, not that difficult, 3 or 4 different ways I think.)
The element does not exist yet when that script is being evaluated. Put it in the body's onload handler or something instead, so it executes once the DOM is in place.
An example of how to do this without touching any markup:
function callWhenLoaded(func) {
if (window.addEventListener) {
window.addEventListener("load", func, false);
} else if (window.attachEvent) {
window.attachEvent("onload", func);
}
}
callWhenLoaded(function() { makeCurrent("undergraduate"); });
The DOM is not fully loaded if you run makeCurrent in your head. You should put that script after your <li> tags.
Your code can be optimized: you can set a class attribute directly with current.className = 'current';.
The reason is that your script is being run before the page load is complete, and therefore before the DOM is populated.
You need to make sure you only call the function after page load is complete. Do this by triggering it using document.onload() or an onload event on the body tag.
After all the technical answers have been spewed out already, I'm going to skip all those which it very well could be and go for some of the more obvious ones I've run into which have caused me to facepalm once I've realised:
Typo in the identity
The identity isn't what you think it is because it's being generated or partially generated by the web framework you're using i.e. in ASP.NET you could set the client id to "MyControl" only to find that by the time it is rendered in the client it's "Page_1$Control_0$MyControl$1"
You've prepended it with a # in one or more of the incorrect places, for instance, although you're not using jQuery in your example if the object id is MyControl, in jQuery and CSS you reference it using #MyControl, but in the actual id of the object, you didn't use #. In document.getElementById() you don't use a # like you would in jQuery and CSS, but you may have used it inadvertently.
You've set the name element in the control instead of the id.
As other people have mentioned though, it could be down to not waiting for the element to be available at the time you're referencing it.