Javascript not finding Button with ID - javascript

In my HTML, I have a simple button defined, like so:
<button id="toggleButton">Stop</button>
I am trying to grab it with the following code:
buttonElement = document.getElementById("toggleButton");
with the goal of assigning an event to it, like so:
buttonElement.onclick = stopTextColor();
The problem is that the getElementById is returning null, even though I can see it in the DOM. What am I doing wrong here?
For clarity, I posted the full code at http://cdpn.io/sqEuH

The problem, probably, is that you're including the JS in the head. What's happening there is the JS is running before the page gets loaded, so the button doesn't show up. Move it to right before the </body> tag, and this problem will be solved, or wrap it with a window.onload() event.

The code you post will work unless the javascript cannot access the given DOM element.
The main possibilities:
The javascript runs before the DOM is parsed (IE if you run it in the head of the document without any code to instruct it to wait till the DOM is ready)
You can usually get around this by placing your script at the bottom of the body rather than in the head or midway through the body. The essential thing to understand here though is that JS can't access an element till the browser has parsed the DOM. The browser parses HTML top-down, and JS scripts run top down, so if you run the JS before the element is parsed, it won't be available to the javascript function yet.
The javascript runs in a context where it can't access the element (inside an iFrame for instance). In this case it would be a question of whether the element is really under the "document" object that you're referring to. If the element is inside an iFrame it will be underneath the iFrame's document object.

Try putting your script just before closing your <body> tag. The DOM is probably not fully loaded when your script is run.
Also, I think you have an error in your Javascript. It should be
buttonElement.onclick = stopTextColor;
instead of
buttonElement.onclick = stopTextColor();
Altough it shouldn't throw any error, it's good practice.
If you want to keep your Javascript before <body>, you can use a listener to wait for the DOM to be loaded and then execute your script, like this :
window.addEventListener("DOMContentLoaded", function() {
buttonElement = document.getElementById("toggleButton");
buttonElement.onclick = stopTextColor;
}, false);
[edit]
The snippet above doesn't work in IE < 9. If you need to support it, use document.load instead, it should give the same result, like so :
document.onload = function() {
buttonElement = document.getElementById("toggleButton");
buttonElement.onclick = stopTextColor;
}
The differece between both, besides browser compatibility, is that window.addEventListener("DOMContentLoaded", function() {...} will fire when the DOM is loaded, but window.load will fire when the DOM AND all other resources (images, stylesheets, etc.) are loaded (slower, and not necessary in your case).

Related

addEventListener on a body element does not get executed

I am using MS Edge in IE11 compatibility mode and have an HTML page in which I have:
<input id="onLoadAttributeHiddenId" type="hidden" value="schadenAuswahl.setCustomCheck();schadenAuswahl.createArrays();">
Further below, I have also:
<script language="JavaScript1.1" src="../js/table_head_uip.js"></script>
And in the table_head_uip.js, I have:
document.body.addEventListener('load', customOnLoadFunction, false);
function customOnLoadFunction(){
var onLoadAttributeFunctStr = document.getElementById("onLoadAttributeHiddenId").value;
var onLoadAttributeFunct = new Function(onLoadAttributeFunctStr);
onLoadAttributeFunct;
}
Now, when I put breakpoints in the table_head_uip.js, the line.
var onLoadFunct = document.body.addEventListener('load', customOnLoadFunction, false);
It gets executed, but the function customOnLoadFunction never gets completed. Also, I do not receive any errors in the console.
Any help will be appreciated.
load events only fire on elements which load things (like an <img> with a src attribute) and the window object (for when the entire document, including its dependencies, has loaded).
The body element doesn't load anything.
The equivalent of the obsolete onload attribute for the body is a load event that fires on the window object. That attribute only existed because, since window isn't an element, you couldn't put attributes on it.
Additionally, the statement onLoadAttributeFunct doesn't do anything. To be useful you need to, for example, put () after it to call it.
new Function(onLoadAttributeFunctStr) is effectively a time delayed eval and is considered dangerous, slow, and hard to debug. You should reconsider the design of your application if you need that.

How to remove HTML script tag with open type [duplicate]

How can I remove script elements before they are being executed?
I thought about using the DOMNodeInserted event, but apparently it doesn't catch script elements. I've also tried using the jQuery livequery plugin like that:
$("script").livequery(function () {
$(this).remove();
});
It did remove the script element, but after it was executed.
I'm looking for a cross-browser solution, but I'm not even sure if that's possible. I read about Mutation Observers which seems close enough but I'm not sure if it can solve my problem.
It would be even better if there was a way to modify the script content before it is being executed without removing and recreating it.
Removing a script element does not do anything. If you can somehow access a script element, it was executed a long time ago and removing it will have no effect.
So we need to work around it. If your script element is at the top of the page like this:
<head>
<script src="yourscript.js"></script>
You could make a synchronous ajax request to the same page, so you can parse its content into a new document, modify all script tags and then replace
the current document with the modified document.
var xhr = new XMLHttpRequest,
content,
doc,
scripts;
xhr.open( "GET", document.URL, false );
xhr.send(null);
content = xhr.responseText;
doc = document.implementation.createHTMLDocument(""+(document.title || ""));
doc.open();
doc.write(content);
doc.close();
scripts = doc.getElementsByTagName("script");
//Modify scripts as you please
[].forEach.call( scripts, function( script ) {
script.removeAttribute("src");
script.innerHTML = 'alert("hello world");';
});
//Doing this will activate all the modified scripts and the "old page" will be gone as the document is replaced
document.replaceChild( document.importNode(doc.documentElement, true), document.documentElement);
Unfortunately this cannot be set up in jsfiddle or jsbin. But you should be able to copy paste this code exactly as it is into this
page's console in google chrome. You should see the alerts and when you inspect the live dom, each script was modified.
The difference is that we are running this after scripts have been executed on the page, so the old scripts should still have a working effect on the page.
That's why, for this to work, you need to be the very first script on the page to do it.
Tested to work in google chrome. Firefox is completely ignoring the doc.write call for some reason.
i donot know what you are trying to do. But it is better to load them on request rather than delete on some conditions.
$.getScript('helloworld.js', function() {
$("#content").html('
Javascript is loaded successful!
');
});
If you wants to remove scripts before there execution, its not possible.
But what you can do is, remove script programatically on a condition & if have an issue with memory-leaks, then you can call below code before remove script.
var var1 = 'hello';
var cleanAll = function () {
delete window.var1;
delete window.cleanAll;
};
// unload all resources
cleanAll();

onload function init not found

I'm encountering a strange issue. I am developing a books application and using javascript onload. I read somewhere that its best to include your javascript at the end of the html. This works for most of the html loaded. However some complain that onload init() not found. This gets solved if i include the javascript in the html head. But than other htmls start behaving strangely. onload gets called before the page is fully loaded. i dont get the correct scroll width. Please suggest what could be worng. Whats the best way of including javascripts. Thanks
html is as follows
columizer id use css column-width which i've defined like this.
css style below
#columnizer
{
width:290px;
height:450px;
column-width:290px;
column-gap:10px;
word-wrap:break-word;
}
Javascript onload is defined like this.
function init()
{
docScrollWidth = document.getElementById('columnizer').scrollWidth;
document.getElementsByTagName('body')[0].style.width = docScrollWidth + "px";
window.external.notify(str);
}
Since the actual answer was in my comment, I'll add that to my answer:
My guess is that you're doing something like window.onload = init(); instead of window.onload = init; and the init function will have to be declared before you do that assignment. You assign function references without the parens. Using the parens causes it to get executed immediately.
You say you're using this code:
docScrollWidth = document.getElementsByTagName('body')[0].style.width
The main problem with this is that style.width ONLY reads a style attribute set directly on the body object. It doesn't get the width of the object as calculated by layout or CSS rules.
So, what you should use instead really depends upon what you're trying to do. The body width will nearly always be the same or more than the window width unless your content is entirely fixed width. So, that makes me wonder what you're trying to accomplish here? What you should use instead depends upon what you're really trying to do.
FYI, document.body is a direct reference to the body object so you don't need document.getElementsByTagName('body')[0].
First, let me define the problem. The window.onload event is used by programmers to kick-start their web applications. This could be something trivial like animating a menu or something complex like initialising a mail application. The problem is that the onload event fires after all page content has loaded (including images and other binary content). If your page includes lots of images then you may see a noticeable lag before the page becomes active. What we want is a way to determine when the DOM has fully loaded without waiting for all those pesky images to load also.
Mozilla provides an (undocumented) event tailor-made for this: DOMContentLoaded. The following code will do exactly what we want on Mozilla platforms:
// for Mozilla browsers
if (document.addEventListener) {
document.addEventListener("DOMContentLoaded", init, false);
}
So what about Internet Explorer?
IE supports a very handy (but non-standard) attribute for the tag: defer. The presence of this attribute will instruct IE to defer the loading of a script until after the DOM has loaded. This only works for external scripts however. Another important thing to note is that this attribute cannot be set using script. That means you cannot create a script using DOM methods and set the defer attribute – it will be ignored.
Using the handy defer attribute we can create a mini-script that calls our onload handler:
<script defer src="ie_onload.js" type="text/javascript"></script>
The contents of this external script would be a single line of code to call our onload event handler:
init();
There is a small problem with this approach. Other browsers will ignore the defer attribute and load the script immediately. There are several ways round this. My preferred method is to use conditional comments to hide the deferred script from other browsers:
<!--[if IE]><script defer src="ie_onload.js"></script><![endif]-->
IE also supports conditional compilation. The following code is the JavaScript equivalent of the above HTML:
// for Internet Explorer
/*#cc_on #*/
/*#if (#_win32)
document.write("<script defer src=ie_onload.js><\/script>");
/*#end #*/
So far so good? We now need to support the remaining browsers. We have only one choice – the standard window.onload event:
// for other browsers
window.onload = init;
There is one remaining problem (who said this would be easy?). Because we are trapping the onload event for the remaining browsers we will be calling the init function twice for IE and Mozilla. To get around this we should flag the function so that it is executed only once. So our init method will look something like this:
function init() {
// quit if this function has already been called
if (arguments.callee.done) return;
// flag this function so we don't do the same thing twice
arguments.callee.done = true;
// do stuff
};
I’ve provided a sample page that demonstrates this technique.

JavaScript AddedToStage equivalent

What is the closest thing to ActionScripts ADDED_TO_STAGE event.
I need to know when a dynamically generated div has been added to another div
var myDiv = document.createElement("div");
$(someContainer).append(myDiv);
If you're using a function such as appendChild to add static text to the DOM, that's a synchronous event. It will be added and rendered by the time your function returns.
If you're appending a child that depends on an external resource, you're looking for the onload event. This works for the main document (window.onload = function() { ... }), and according to What html tags support the onload/onerror javascript event attributes?, body, frame, frameset, iframe, img, link and script. (They apparently get their information from http://www.w3schools.com/jsref/event_onload.asp, which is not nearly as good as straight from the spec, but I couldn't find the details in there.)

My code gives me an error message: GetElementById() is null or not an object

I have this js code:
var id = document.getElementById("myDiv").getAttribute("data-id");
et="Your Message Here";
el="http://x2.xclicks.net/sc/out.php?s="+id+""
sl=new Array();
sn=new Array();
a="</a>"; af="<a target='_blank'";
function dw(n) {document.write(n,"\n");}
function showLink(n,s,b){
if(!s) {s='anc'}
if(!b) {b=''}
else {b="&b="+b}
ast = af+" class='"+s+"' href='"+el;
n = n-1;
if(sl[n]&&sl[n]!="") {
dw(ast+"&o="+sl[n]+b+"'>"+sn[n]+a)
} else {
dw(ast+b+"'>"+et+a)
}
}
Which I load in my header.php like this:
<script type="text/javascript" src="<? bloginfo('template_url'); ?>/js/trf.js"></script>
The problem is that although this is correct:
var id = document.getElementById("myDiv").getAttribute("data-id");
I get this error:
getElementById() is null or not an object
Ady Ideas why?
Do I need to declare a document ready or something?
Do I need to declare a document ready or something?
Yes, exactly. Before the document is ready (ie all tags are parsed to DOM elements), you won't be able to get elements by id. This would only work for elements above your script tag, which are already parsed. Moving the script inclusion from <head> before the end of </body> would help. Alternatively you'll need to use one of the various DOMContentLoaded or onload events, which unfortunately are not cross-browser supported. I recommend to search for a good snippet or use a library.
Assuming you're loading that script in the <head> of your document, you are trying to get an element by ID when that element is not yet loaded into the DOM.
You will need to wait for your document to be ready (via onDOMContentLoaded, window.onload, or any other way of deferring until rendering is complete) in order to access that element by ID.
I would try wrapping it in a $(document).ready. More than likely you're just trying to access it before the DOM is ready
You're loading the script in the header, which means that the script is being loaded before the rest of the document. Inside the script, you're calling document.getElementById straight away, and since the rest of the document hasn't finished loading the chances are extremely high the element you're after won't exist yet.
You need to delay running that part of the script until the document is fully loaded. Wrap that part of the script in a function, and call it during the body.onload event.
As an example (there are other ways to achieve the same result):
window.document.onload = function(e){
var id = document.getElementById("myDiv").getAttribute("data-id");
// Now you have the id and can do whatever you want with it.
}

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