Exactly when does an IFRAME onload event fire?

Does the IFRAME's onload event fire when the HTML has fully downloaded, or only when all dependent elements load as well? (css/js/img)

The latter: <body onload= fires only when all dependent elements (css/js/img) have been loaded as well.

If you want to run JavaScript code when the HTML has been loaded, do this at the end of your HTML:

<script>alert('HTML loaded.')</script></body></html>

Here is a relevant e-mail thread about the difference between load and ready (jQuery supports both).

The above answer (using onload event) is correct, however in certain cases this seems to misbehave. Especially when dynamically generating a print template for web-content.

I try to print certain contents of a page by creating a dynamic iframe and printing it. If it contains images i cant get it to fire when the images are loaded. It always fires too soon when the images are still loading resulting in a incomplete print:

function printElement(jqElement){
    if (!$("#printframe").length){
        $("body").append('<iframe id="printframe" name="printframe" style="height: 0px; width: 0px; position: absolute" />');
    }

    var printframe = $("#printframe")[0].contentWindow;
    printframe.document.open();
    printframe.document.write('<html><head></head><body onload="window.focus(); window.print()">');
    printframe.document.write(jqElement[0].innerHTML);
    printframe.document.write('</body></html>');
//  printframe.document.body.onload = function(){
//      printframe.focus();
//      printframe.print();
//  };
    printframe.document.close();
//  printframe.focus();
//  printframe.print();

//  printframe.document.body.onload = function()...
}

as you can see i tried out several methods to bind the onload handler... in any case it will fire too early. I know that because the browser print preview (google chrome) contains broken images. When I cancel the print and call that function again (images are now cached) the print preview is fine.

... fortunately i found a solution. not pretty but suitable. What it does that it scans the subtree for 'img' tags and checking the 'complete' state of those. if uncomplete it delays a recheck after 250ms.

function delayUntilImgComplete(element, func){
    var images = element.find('img');
    var complete = true;
    $.each(images, function(index, image){
        if (!image.complete) complete = false;
    });
    if (complete) func();
    else setTimeout(function(){
        delayUntilImgComplete(element, func);}
    , 250);
}    

function printElement(jqElement){
    delayUntilImgComplete(jqElement, function(){
        if (!$("#printframe").length){
            $("body").append('<iframe id="printframe" name="printframe" style="height: 0px; width: 0px; position: absolute" />');
        }

        var printframe = $("#printframe")[0].contentWindow;
        printframe.document.open();
        printframe.document.write(jqElement[0].innerHTML);
        printframe.document.close();
        printframe.focus();
        printframe.print();
    });
}

Just when the html loads, not the dependent elements. (or so I think).

To fire when the rest of the page loads do jQuery(window).load(function(){ or window.onload not document onready.

You can also check to see if an image element is loaded and there... if image . load-- etc.

来源：https://stackoverflow.com/questions/815263/exactly-when-does-an-iframe-onload-event-fire

标签

javascript

html

iframe

onload