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從Stack Overflow學前端系列 第 12

從StackOverflow上學CODING(12)與jQuey 的$(document).ready 相同的語法

$(document).ready equivalent without jQuery

I have a script that uses $(document).ready, but it doesn't use anything else from jQuery. I'd like to lighten it up by removing the jQuery dependency.
我目前有一個JS檔正在用$(document).ready,但是我目前想要拿掉jQuery
How can I implement my own $(document).ready functionality without using jQuery? I know that using window.onload will not be the same, as window.onload fires after all images, frames, etc. have been loaded.
在此情況下我該如何應用才能不使用jQuery達到同樣的功能呢?我知道window.onload一定不一樣


There is a standards based replacement,DOMContentLoaded that is supported by over 98% of browsers, though not IE8:
有一個標準的用法DOMContentLoaded,98%的瀏覽器都支援,除了IE8:

document.addEventListener("DOMContentLoaded", function(event) { 
  //do work
});

jQuery's native function is much more complicated than just window.onload, as depicted below.
jQuery的原生函式比window.onload複雜非常多,如下所述:

function bindReady(){
    if ( readyBound ) return;
    readyBound = true;

    // Mozilla, Opera and webkit nightlies currently support this event
    if ( document.addEventListener ) {
        // Use the handy event callback
        document.addEventListener( "DOMContentLoaded", function(){
            document.removeEventListener( "DOMContentLoaded", arguments.callee, false );
            jQuery.ready();
        }, false );

    // If IE event model is used
    } else if ( document.attachEvent ) {
        // ensure firing before onload,
        // maybe late but safe also for iframes
        document.attachEvent("onreadystatechange", function(){
            if ( document.readyState === "complete" ) {
                document.detachEvent( "onreadystatechange", arguments.callee );
                jQuery.ready();
            }
        });

        // If IE and not an iframe
        // continually check to see if the document is ready
        if ( document.documentElement.doScroll && window == window.top ) (function(){
            if ( jQuery.isReady ) return;

            try {
                // If IE is used, use the trick by Diego Perini
                // http://javascript.nwbox.com/IEContentLoaded/
                document.documentElement.doScroll("left");
            } catch( error ) {
                setTimeout( arguments.callee, 0 );
                return;
            }

            // and execute any waiting functions
            jQuery.ready();
        })();
    }

    // A fallback to window.onload, that will always work
    jQuery.event.add( window, "load", jQuery.ready );
}

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