How to tell if the window.onload event has already fired?

B

Brian

Hi everyone,

I'm writing a function (in javascript) that needs to do one thing if
the page has not loaded, and another (different) thing if the page has
already loaded.

I'm looking for a way to tell if the window.onload event has already
fired. I cannot edit the onload event handler itself, and my function
can only exist in an external js file, sourced from the document's
head section. Any ideas?

Thanks,
Brian
 
B

Blue Raja

Brian said:
Hi everyone,

I'm writing a function (in javascript) that needs to do one thing if
the page has not loaded, and another (different) thing if the page has
already loaded.

I'm looking for a way to tell if the window.onload event has already
fired. I cannot edit the onload event handler itself, and my function
can only exist in an external js file, sourced from the document's
head section. Any ideas?
Click to expand...

How about:

src.js
[STARTFILE]
var hasLoaded = false;

function myfunc(/* param list */){
if (hasLoaded){
// do post-load stuff here
} else {
// do pre-load stuff here
}
}
[ENDFILE]

file.html
[STARTFILE]
<html>
<!-- head declaration -->
<body onload="hasLoaded = true;">
<!-- body stuff -->
</body>
</html>
[ENDFILE]

Hope that helps.
 
G

Grant Wagner

Mick said:
...
window.onload=myFunc
</script>
</head>
<body>
...
Click to expand...

And if the onload event is already defined on the page, that line, if placed
in the <head>, will be replaced by the onload event defined in the <body>. If
placed in the <body>, it will replace any existing onload event for the page.

Injecting code for execution onload when you have no other control over the
page is problematic at best. The following works in IE6SP1, Firefox 0.9.1,
Mozilla 1.7, Opera 7.5.2 and Netscape 4.78 on an x86 under Windows XP. I make
no claims about other browsers on other platforms.

<head>
<script type="text/javascript">
function appendOnloadEvent(eventHandler) {
if (window.onload) {
// there is currently an onload event defined for
// window; append the event handler javascript to
// the current event handler javascript
window.onload = new Function(
// take the original event
window.onload
// convert it to a string; the string looks like:
// "...function...()...{...[js]...}..."
.toString()
// remove any newlines or carriage returns
.replace(/[\r\n]/g, '')
// remove any leading or trailing whitespace
.replace(/\s+$|^\s+/g, '')
// turn "function...()...{...[js]...}"
// into "function...()...{...[js][newline][new js]...}"
.replace(
/^function\s*\w+\s*\(\w*\)\s*\{\s*(.*)\s*\}$/,
'$1\n' + eventHandler
)
);
} else {
// there is currently no onload event defined for this
// window; set the event handler javascript to handle
// the event
window.onload = new Function(eventHandler);
}
}

function test() {
alert('bye');
}
</script>
</head>

<body onload="alert('hi');">
<script type="text/javascript">appendOnloadEvent('test();');</script>
</body>

But even it requires script injection inside the <body></body> to work
properly.
 
M

Mick White

Grant said:
Mick White wrote:




And if the onload event is already defined on the page, that line, if placed
in the <head>, will be replaced by the onload event defined in the <body>. If
placed in the <body>, it will replace any existing onload event for the page.
Click to expand...
I assumed that that the onload event was not pre-assigned.
See my comments below.

Injecting code for execution onload when you have no other control over the
page is problematic at best. The following works in IE6SP1, Firefox 0.9.1,
Mozilla 1.7, Opera 7.5.2 and Netscape 4.78 on an x86 under Windows XP. I make
no claims about other browsers on other platforms.

<head>
<script type="text/javascript">
function appendOnloadEvent(eventHandler) {
if (window.onload) {
// there is currently an onload event defined for
// window; append the event handler javascript to
// the current event handler javascript
window.onload = new Function(
// take the original event
window.onload
// convert it to a string; the string looks like:
// "...function...()...{...[js]...}..."
.toString()
// remove any newlines or carriage returns
.replace(/[\r\n]/g, '')
// remove any leading or trailing whitespace
.replace(/\s+$|^\s+/g, '')
// turn "function...()...{...[js]...}"
// into "function...()...{...[js][newline][new js]...}"
.replace(
/^function\s*\w+\s*\(\w*\)\s*\{\s*(.*)\s*\}$/,
'$1\n' + eventHandler
Click to expand...

Grant, this is remarkable, a novel approach, indeed.
 
L

Lee

Brian said:
Hi everyone,

I'm writing a function (in javascript) that needs to do one thing if
the page has not loaded, and another (different) thing if the page has
already loaded.

I'm looking for a way to tell if the window.onload event has already
fired. I cannot edit the onload event handler itself, and my function
can only exist in an external js file, sourced from the document's
head section. Any ideas?
Click to expand...

This seems to work in IE66, Netscape 7.1 and family, and Opera 7.51,
either in the head or in an external .js file.
The Mozillas execute the new handler first, the others execute
it after the original handler.

<html>
<head>
<script type="text/javascript">
function myHandler(){alert("Loaded")}
if(window.addEventListener){
alert("window.addEventListener");
window.addEventListener("load",myHandler,false);
}else if(window.attachEvent){
alert("window.attachEvent");
window.attachEvent("onload",myHandler);
}else{
alert("None of the above");
}
</script>
</head>
<body onload="alert('original onload handler')">
<script type="text/javascript">alert("loading")</script>
done
</body>
</html>
 

Ask a Question

Want to reply to this thread or ask your own question?

You'll need to choose a username for the site, which only take a couple of moments. After that, you can post your question and our members will help you out.

Ask a Question

Similar Threads

Can script determine if window.onload has already fired? 55
Can someone tell me if this a real tracker? Or is it one designed to show you a different message at certain times, ie. acting like one? 0
window.onload and extern js 7
Synchronizing multiple AJAX calls in window.onload() event 5
How do I push into an array using an event listener? 5
window.onload fails from external JS file 17
How to use PDF-lib and how to center each line of texts on the page? 1
window.onload being ignored for child in IE 2

Members online

Total: 42 (members: 1, guests: 41)
Robots: 312

Forum statistics

Threads
473,755
Messages
2,569,536
Members
45,012
Latest member
RoxanneDzm

Latest Threads

Top