This question already has answers here:
Why does jQuery or a DOM method such as getElementById not find the element?
(6 answers)
Closed 9 years ago.
I'm trying to get the element with getElementById(), but it returns null even though the element exists. What am I doing wrong?
<html>
<head>
<title>blah</title>
<script type="text/javascript">
alert(document.getElementById("abc"));
</script>
</head>
<body>
<div id="abc">
</div>
</body>
You have to put this in a document load event. The DOM hasn't gotten to abc by the time the script is executed.
Your script runs before the DOM has been loaded. To fix this you can place your code in the window.onload function like so:
window.onload = function() {
alert(document.getElementById("abc"));
};
An alternative is to place your script right before the closing </body> tag.
If you don't want to attach to the load event then simply put your script at the bottom of the body, so it will execute at the end-
<html>
<head>
<title>blah</title>
</head>
<body>
<div id="abc">
</div>
<script type="text/javascript">
alert(document.getElementById("abc"));
</script>
</body>
</html>
This is because the script runs before the page has rendered.
For proof add this attribute to the body tag:
<body onload="alert(document.getElementById('abc'));" >
But it doesn't exist, not at that point in the HTML. HTML documents are parsed top-to-bottom, just like programs run. The best solution is just to put your script tag at the bottom of the page. You could also attach your JavaScript to the onload event.
Related
This question already has answers here:
Why does jQuery or a DOM method such as getElementById not find the element?
(6 answers)
document.getElementById() doesn't work? [duplicate]
(7 answers)
Closed 7 years ago.
im new to javascript and want to fill a div with some text. but it doesn't work.
in the documentation this is the common way to do this. but, why doesn't work this for me?
my code is
<!DOCTYPE html>
<html>
<head>
<title></title>
<script type="text/javascript">
document.getElementById('mytest').innerHTML="hey";
</script>
</head>
<body>
<div id="mytest"></div>
</body>
</html>
You need to move your script to the end of your HTML. Right now, you're executing the script BEFORE your HTML has been parsed so the document is empty and thus document.getElemntById('mytest') does not find anything.
<!DOCTYPE html>
<html>
<head>
<title></title>
</head>
<body>
<div id="mytest"></div>
<script type="text/javascript">
document.getElementById('mytest').innerHTML="hey";
</script>
</body>
</html>
See this other answer for a lot more discussion of this issue and other options if you don't want to move your <script> tag:
pure JavaScript equivalent to jQuery's $.ready() how to call a function when the page/dom is ready for it
thats because, in your document, the javascript is load at the first, but the div with the id mytest is not loaded at this moment.
you have 2 options to get this working:
first: say javascript to wait until the dom is loaded completly
window.onload=function(){
document.getElementById('mytest').innerHTML="hey";
}
second:
put your script code at the bottom, so the javascript is loaded at least.
but i would prefer the first solution.
best
Try in this way
<!DOCTYPE html>
<html>
<head>
<title></title>
</head>
<body>
<div id="mytest"></div>
</body>
<script type="text/javascript">
document.getElementById('mytest').innerHTML="hey";
</script>
</html>
Js fiddle
I was told to add a tag being generated in Joomla. I just need to add the onload=... between the body tags. Is there a way to add the onload=... by itself or must it be part of the tag? Thanks!
If I understand the question correctly, and you need to trigger some JavaScript to run after the document is ready without editing the body tag itself, you could add it as follows:
<script>
jQuery(document).ready(function() {
// Your code
}
</script>
Notice the lack of "$". In Joomla, avoid using $ to reference jQuery to prevent conflicts with other JS tools.
If I've completely missed the mark, please clarify in a comment.
You can bind the event handler with JavaScript.
<script>
addEventListener('load', yourFunction);
function yourFunction(event) {
// ...
}
</script>
If you add a <script> tag to the header of the page, you can then add an event listener for the page load. Or a better option is to prevent render blocking code and add the <script> tag to the bottom of the page and have it run right away, since the page is already loaded.
Render Blocking Method
<html>
<head>
<script>
window.addEventListener('load',pageLoaded,false);
function pageLoaded(e) { console.log('Loaded'); }
</script>
</head>
<body>
</body>
</html>
Non Render Blocking
<html>
<head>
</head>
<body>
<!-- All The Body Content -->
<script>
(function() {
console.log('Loaded');
})();
</script>
</body>
</html>
This question already has answers here:
when and where to put javascript in html
(7 answers)
Closed 9 years ago.
the thing is i'm unable to figure out where to embed javascript in html page whether in head section or body section.
example 1:
<html>
<head>
<title>events</title>
<script>
document.getElementById("b").onclick=function(){displayDate()};
function displayDate()
{
document.getElementById("demo").innerHTML=Date();
}
</script>
</head>
<body>
<p id="demo"></p>
<button id="b">new</button>
</body>
</html>
in the above example I placed script tags in head section but it is not working.
example: 2
<html>
<head>
<title>events</title>
<script>
function upper()
{
var x=document.getElementById("t");
x.value=x.value.toUpperCase();
}
</script>
</head>
<body >
enter some text:<input type="text" id="t" onChange="upper()"/>
</body>
</html>
in the second example I placed the javascript in head section it is working properly.first example demonstrates that on clicking a button date will be displayed in the second example in a text box when data is entered and if we come out of the box the letters in the box will we converted to uppercase.
To have it more readable I prefer to always place JavaScript in the head section. If you need to access elements from there, use the window.onload event:
<head>
<title>events</title>
<script type="text/javascript">
window.onload = function() {
document.getElementById("b").onclick = function() {
displayDate();
};
};
function displayDate()
{
document.getElementById("demo").innerHTML=Date();
}
</script>
</head>
This would work just fine.
Your second example worked because you just defined a function, you didn't try to access any element.
You can put it in the head. The problem is that your examples are not the same. The first one doesn't work because the current date is retrieved by calling Date(), when it should be new Data().getDate(). The second example works because the code is valid.
The problem you're running into is that you're trying to reference an element before it is loaded into the DOM.
When you're putting the script in the HEAD tag, the dom hasn't been loaded yet and the document.getElementById won't find what you're looking for.
You have a few different options to deal with this. You can put the script at the end of the page, which will work for your small example here.
Probably a better option is to take a look at learning/using jquery or another js utility. Jquery makes it easy to solve this issue by giving you a "ready" event. This ready event will be triggered when the DOM is fully loaded. So:
$(document).ready(
function()
{
$("#demo").html((new Date()).toString());
});
Is all you really need. With this approach, it doesn't matter where the script it on the page.
I am not clear why its not working the javascript code when I add it to the header section as follows.
We can place a javascript code within the body as follows
<html>
<head>
<title> Simple Test </title>
</head>
<body>
<div id="mydiv"> This is the div content </div>
<script type="text/javascript" >
document.getElementById("mydiv").innerHTML=Date();
</script>
</body>
</html>
But when I place the same JavaScript code in the header section it doesn't work.
<html>
<head>
<title> Simple Test </title>
<script type="text/javascript" >
document.getElementById("mydiv").innerHTML=Date();
</script>
</head>
Can Someone please explain the issue. I know I can Write a JavaScript function in header and call it in an event. But can't we Use in this way. If Can't why.
<html>
<head>
<title> Simple Test </title>
<script type="text/javascript" >
window.onload= function (){document.getElementById("mydiv").innerHTML=Date();}
</script>
</head>
I think above code will help you to solve your problem. You can try this one.
because when the page is loaded, by the time the browser gets to that <script> element, the #mydiv element has not yet been created.
either use an "onload" event, or put your scripts at the bottom of the page.
It's because the page is being rendered in the order it's read. Therefore when the script in the header is evaluated the rest of the page hasn't been rendered yet (ie the myDiv element hasn't been created).
When you create an event handler in the head that works fine - the handler is set up before the rest of the page is loaded but the event can't happen until the element exists.
When you put it in the <head>, it runs before the <body> exists.
this is because of the page rendering order.you can access elements before it has been created. if you can, try to put all JavaScript code end of the page(before closing body tag). it will save your page load time. if you cannot put it in the bottom, put the code inside onload event.
i use that tag to alert me when a tag has been shows up
<html>
<head>
</head>
<body>
<script type="text/javascript">
document.getElementsByTagName('iframe')[0].onload = function() {
alert('loaded');
}
</script>
<iframe></iframe>
</body>
</html>
strange , since this code working :
<html>
<head>
</head>
<body>
<iframe></iframe>
<script type="text/javascript">
document.getElementsByTagName('iframe')[0].onload = function() {
alert('loaded');
}
</script>
</body>
</html>
why the Js need to under the tag to work?
what's the problem here?
Because the code in a script tag is executed immediately. And in the first example the iframe doesn't exist at that time. But what you can do is to wrap you code into an onload (for the main page) event. E.g.:
window.onload = function() {
//your code
}
Then it doesn't matter where the code is placed.
Iframe tag does not exist at the moment you are trying to access it.
You may check that by simply alerting array length, like
alert(document.getElementsByTagName('iframe'));
Have you thought about executing your javascript after the page is loaded? You may use some frameworks like jQuery to facilitate crossbrowser issues. Or just put all your javascript code to the very bottom of body.