I have a JS script which created a new Node and inserts it to the HTML page. I am handling DOM mutation events and can capture DOMNodeInserted event. Inside that function I want to find out the source (i.e. in which part of the HTML has the script function been called) and the target (i.e. in which part the node is being added in the HTML page).
I am able to find the target using event.target, but I am not able to find the source of the event.
For example, consider the following pseudocode HTML page:
<html>
<head>
<script>
function test() {
//DOM access
<div_object>.setAttribute("attr", "value");
}
</script>
</head>
<body onload="test()">
<div id="123">
</div>
</body>
</html>
I want my source to be BODY (because that is were the script is initiated), target should be div(123) (because the attribute is added to div_123.
How can I do this?
Sorry, you can't find out what piece of code caused an event to be triggered, they're completely decoupled. You would have to have the triggering code co-operate by storing the values of its own this/event.target in a variable for the triggered code to pick up later.
But then if you have co-operation like that, you wouldn't need DOM Mutation Events.
If you have an event handling layer (as is part of many JS frameworks), you could put the this/target tracking in that layer, so the triggered code could ask “what was the last event that fired, before me?”.
But I'm not convinced this would be worth it. It's usually best to add your own co-operative hooks that communicate between components; you can't generally rely on DOM Mutation Events since they're not globally and completely supported (or indeed supported at all on IE<9).
What about
<html>
<head>
<script>
function test(element) {
//DOM access
element.setAttribute("attr", "value");
}
</script>
</head>
<body onload="test(this)">
<div id="123">
</div>
</body>
</html>
?
Interesting. I had a look here (answered to get formatting)
<html>
<head>
<script>
function test(e) {
if (e) var event=e;
//DOM access
var t="";
for (o in event) t+='<br/>'+o+':'+event[o]
document.getElementById('d123').innerHTML=t;
}
</script>
</head>
<body onload="test(event)">
<div id="d123">
</div>
</body>
</html>
Related
I have tried finding an answer to this on my own, but only found instructions on how to use onload events. I seem to be missing the point.
I've been taught that if I want something to happen when the page loads, I should use window.onload like this:
<script>
window.onload = dosomething();
function dosomething()
{
window.alert('hello');
}
</script>
But now that I am thinking on my own I wonder what the point of doing that is. Because this also produces the same result:
<script>
dosomething();
function dosomething()
{
window.alert('hello');
}
</script>
Anything I put at the top inside <script> is going to execute anyway... so what's the point of window.onload?
If you're directly running your code with dosomething();, you're delaying your browser's rendering for the time it takes your JavaScript code to run.
You can try to insert your code to the <head> of your html document:
<!DOCTYPE html>
<html>
<head>
<script>
dosomething();
function dosomething()
{
window.alert('hello');
}
</script>
</head>
<body>
Does not render before the alert is dismissed!
</body>
</html>
You'll see that the page stays blank until you dismiss the alert. So every second the browser takes to run your JavaScript code is a second that your users have to wait for the site to be rendered.
Now if you change the code to be run on body's onload, the page gets rendered before the alert is shown:
<!doctype html>
<html>
<head>
<script>
function dosomething()
{
window.alert('hello');
}
</script>
</head>
<body onload="dosomething()">
This page gets rendered before the alert!
</body>
</html>
Consider these two blocks of code:
<head>
<script>
alert(document.getElementById('foo').value);
</script>
</head>
<body>
<input id="foo" value="hello">
</body>
<head>
<script>
window.onload = function() {
alert(document.getElementById('foo').value);
}
</script>
</head>
<body>
<input id="foo" value="hello">
</body>
In the first example, we'll get an error because the element you are referencing isn't found when the script runs - and so you are trying to get value of null.
In the second example, document.getElementById() will find the element with the id foo, because window.onload will get fired only when the complete DOM has been loaded and so the element is available.
window.onload will fire once the DOM has finished loading. In your example, the DOM is not required. However, the following code will fail if the DOM has not yet loaded:
function doSomething() {
alert(document.getElementById('test').innerText);
}
// Throws: TypeError: Cannot read property 'innerText' of null
Assuming your page contains an element with id test, it will alert its text.
waiting for the onload event assures you that all of your scripts and resources are loaded
Assume you are using jquery in your page and you invoked a function that uses it directly without onload , you can't guarantee that the jquery file has been loaded, which will lead to errors and possibly ruining your whole logic
The onload event is handy to make sure the page is fully loaded before you run a script. For your example above it doesn't make sense, but if your page is still loading an item on the bottom and you try to call it then nothing will run.
I recommend using jQuery and using the ready function. This way you will ensure your page is completely loaded.
$( document ).ready(function() {
// This will only run after the whole page is loaded.
});
If you don't want to load query, just put your javascript at the bottom of the page. It's best practice, and ensures the DOM is loaded in full.
For more info on the jquery ready function go here: https://api.jquery.com/ready/
I have read that if you want to make it look like your site loads faster then you should put your javascript at the end of your html file like the following
<html>
<body>
</body>
<script>
//my awesome javascript functions go here because it lets things load faster
//than if it was at the top
</script>
</html>
The problem is when I create buttons or use onChange events that call these functions.
How am I meant to keep my JS at the bottom of the page and have the JS defined for when it reads that the js function will need to be called?
For example
<html>
<body>
<input type="text" onChange="myfunction()"/>
</body>
<script>
function myfunction(){}
</script>
</html>
I did the code in pseudo code-ishly so you wouldn't focus on any of my syntax errors, but more focus on how I am meant to go about this.
When creating the page, it creates the html properly, but gives me a console error saying "myfunction" is not defined.
If I move the script part above the body this works, but it is recommended to keep it last to increase speed in page load.
Just a note I am not using jquery.
I originally thought this was a duplicate (Javascript at the bottom, function call in the body?) but it doesn't seem to answer my problem.
------------------------update----------------------------
using event listeners
<html>
<body>
<input type="text" id="myawesometext"/>
</body>
<script>
function myfunction(){}
element = document.getElementById('myawesometext');
element.addEventListener("onChange", myfunction, false);
</script>
</html>
I have this function which is trying to change the src property of an img. Here's the Javascript:
function transition(){
document.getElementById("firstfirst").src = marray[currArrayValue];
currArrayValue++;
if(currArrayValue == array.length-1){
currArrayValue = 0;
}
setTimeout(transition(), 1000);
}
My google chrome console is saying document.getElementById("firstfirst") doesn't exist, but it definitely does. Here's the HTML:
<div id="banners-container">
<div id="banners">
<img src="images/banners/top-banner-one.png" id="firstfirst" alt="Subscribe now to get access to thousands of vintage movies!" border="0">
</div>
</div>
What gives?
Javascript is executed as soon as it has been parsed.
If your JS is included in the <head> of your webpage, it will be executed before the document body has been parsed and the DOM has been built.
As such, you need to engineer your code so that it is not executed until the DOM has been loaded. You might want to look at the MDN docs on the DomContentLoaded event. Alternatively, you can use one of the many JavaScript libraries out there which wrap this up for you.
if chrome says the element is null it is null. Perhaps you are calling function before the element loaded in DOM. like calling the function in head tag prior the element tag.
so try something like this.
<html>
<head>
<script>
function F () { /*reach element*/ }
</script>
</head>
<body>
//The element
</body>
<script>
F ();
</script>
</html>
How do I add text/elements to a target element (div) using getElementById (without jquery) when the page loads?
Here's my markup currently:
<html>
<head>
<title>test</title>
<script language="javascript">
/document.getElementById('content').innerHTML = 'Fred Flinstone';
</script>
</head>
<body>
<div id="content">
dssdfs
</div>
</body>
</html>
<script type="text/javascript">
function dothis()
{
document.getElementByID('content').innerHTML = 'Fred Flinstone';
}
</script>
<body onLoad="dothis()">
...
</body>
I think what is happening is that your script is executing before your document is ready. Try placing your javascript in a body load event.
The quickest (although not the best) way to do it is to put your script block towards the end of the HTML file (after the <div> you wish to modify).
The better way to do it is to register for DOM load notification
If you want it to execute after the page loads, then you need to observe the DOM loaded event. You can do that by subscribing to the DOM load event in the script block and then put the code that manipulates the DIV in the event handler.
The tricky part is that different browsers may need slightly different ways to register to be notified when the DOM is loaded (that's were jQuery or a different library becomes useful)
Here's some more information about different ways to register for a callback to be called when the DOM is loaded. The information may be a bit out of date as more modern versions of the popular browsers have become more standards compliant now: http://www.javascriptkit.com/dhtmltutors/domready.shtml
I'm trying to write a javascript function that adds some DOM nodes to the document in the place it was called, like this:
...
<div>
<script type="text/javascript">
pushStuffToDOMHere(args);
</script>
</div>
...
i try to do it 'cleanly', without using node id property of the div, or innerHTML string manipulation. for that I need to know where in the document the script tag is located.
is there a way to do it?
Talking about cleanly, I don't think your approach is particularly clean. It is a much better idea to give the div a unique id and execute your javascript when the DocumentReady-event fires.
Do you have an overriding reason for doing it this way? If not the suggestion to use a unique id makes the most sense. And you can always use a library like jQuery to make this even easier for yourself.
However, the following quick test shows that if you use document.write() in the function then it writes the value into the place where the function was called from.
<html>
<head>
<script type="text/javascript">
function dosomething(arg){
document.write(arg);
}
</script>
</head>
<body>
<div>The first Div</div>
<div>The
<script type="text/javascript">
dosomething("Second");
</script>
Div
</div>
<div>The
<script type="text/javascript">
dosomething("Third");
</script>
Div
</div>
</body>
</html>
But, again the question, are you sure this is what you want to do?
Although I agree with n3rd and voted him up, I understand what you are saying that you have a specific challenge where you cannot add an id to the html divisions, unless by script.
So this would be my suggestion for inlining a script aware of its place in the DOM hierarchy, in that case:
Add an id to your script tag. (Yes, script tags can have ids, too.)
ex. <script id="specialagent" type="text/javascript">
Add one line to your inline script function that gets the script element by id.
ex. this.script = document.getElementById('specialagent');
...And another that gets the script element's parentNode.
ex. var targetEl = this.script.parentNode;
Consider restructuring your function to a self-executioning function, if you can.
Ideally it executes immediately, without the necessity for an 'onload' call.
see summary example, next.
SUMMARY EXAMPLE:
<script id="specialagent" type="text/javascript">
var callMe = function(arg1,arg2,arg3) {
this.script = document.getElementById('specialagent');
var targetEl = this.script.parentNode.nodeName=="DIV" && this.script.parentNode;
//...your node manipulation here...
}('arg1','arg2','arg3');
</script>
The following TEST code, when run, proves that the function has identified its place in the DOM, and, importantly, its parentNode. The test has division nodes with an id, only for the purpose of the test. They are not necessary for the function to identify them, other than for testing.
TEST CODE:
<html>
<head>
<title>Test In place node creation with JS</title>
</head>
<body>
<div id="one">
<h2>Child of one</h2>
<div id="two">
<h2>Child of two</h2>
<script id="specialagent" type="text/javascript">
var callMe = function(arg1,arg2,arg3) {
this.script = document.getElementById('specialagent');
var targetEl = this.script.parentNode;
/*BEGIN TEST*/
alert('this.script.id: ' + this.script.id);
alert('targetEl.nodeName: ' + targetEl.nodeName + '\ntargetEl.id: '+targetEl.id);
alert('targetEl.childNodes.length: ' + targetEl.childNodes.length);
var i = 0;
while (i < targetEl.childNodes.length) {
alert('targetEl.childNodes.'+i+'.nodeName = ' + targetEl.childNodes[i].nodeName);
++i;
}
/*END TEST - delete when done*/
//...rest of your code here...to manipulate nodes
}('arg1','arg2','etc');
</script>
</div>
</div>
</body>
</html>
Not really sure what your trying to achieve but this would pass the dom element to the function when clicked. You could then use jquery in the function to do what you wanted like so
...
<script type="text/javascript">
function pushStuffToDOMHere(element)
{
$(element).append("<p>Hello</p>"); // or whatever
}
</script>
<div onclick="pushStuffToDOMHere(this);">
</div>
...
my solution is a compbination of the (good) answers posted here:
as the function is called, it will document.write a div with a unique id.
then on document.onload that div's parent node can be easily located and appended new children.
I chose this approach because some unique restrictions: I'm not allowed to touch the HTML code other than adding script elements. really, ask my boss...
another approach that later came to mind:
function whereMI(node){
return (node.nodeName=='SCRIPT')? node : whereMI(node.lastChild);
}
var scriptNode = whereMI(document);
although, this should fail when things like fireBug append themselves as the last element in the HTML node before document is done loading.