<img src="images/placeholder.png" lazy-src="images/realimg.jpg" alt="" />
<!-- 如果瀏覽器禁用了js，我們也不能不讓網(wǎng)頁顯示圖片撒，所以最好是加上下面一句備用代碼 -->
<noscript><img src="images/realimg.jpg" alt="" /></noscript>

圖片延遲加載插件代碼
(function( $ ){
$.fn.imglazyload = function( options ){
var o = $.extend({
attr : 'lazy-src',
container : window,
event : 'scroll',
fadeIn : false,
threshold : 0,
vertical : true
}, options ),
event = o.event,
vertical = o.vertical,
container = $( o.container ),
threshold = o.threshold,
// 將jQuery對象轉(zhuǎn)換成DOM數(shù)組便于操作
elems = $.makeArray( $(this) ),
dataName = 'imglazyload_offset',
OFFSET = vertical ? 'top' : 'left',
SCROLL = vertical ? 'scrollTop' : 'scrollLeft',
winSize = vertical ? container.height() : container.width(),
scrollCoord = container[ SCROLL ](),
docSize = winSize + scrollCoord;
// 延遲加載的觸發(fā)器
var trigger = {
init : function( coord ){
return coord >= scrollCoord &&
coord <= ( docSize + threshold );
},
scroll : function( coord ){
var scrollCoord = container[ SCROLL ]();
return coord >= scrollCoord &&
coord <= ( winSize + scrollCoord + threshold );
},
resize : function( coord ){
var scrollCoord = container[ SCROLL ](),
winSize = vertical ?
container.height() :
container.width();
return coord >= scrollCoord &&
coord <= ( winSize + scrollCoord + threshold );
}
};
var loader = function( triggerElem, event ){
var i = 0,
isCustom = false,
isTrigger, coord, elem, $elem, lazySrc;
// 自定義事件只要觸發(fā)即可，無需再判斷
if( event ){
if( event !== 'scroll' && event !== 'resize' ){
isCustom = true;
}
}
else{
event = 'init';
}
for( ; i < elems.length; i++ ){
isTrigger = false;
elem = elems[i];
$elem = $( elem );
lazySrc = $elem.attr( o.attr );
if( !lazySrc || elem.src === lazySrc ){
continue;
}
// 先從緩存獲取offset值，緩存中沒有才獲取計(jì)算值,
// 將計(jì)算值緩存，避免重復(fù)獲取引起的reflow
coord = $elem.data( dataName );
if( coord === undefined ){
coord = $elem.offset()[ OFFSET ];
$elem.data( dataName, coord );
}
isTrigger = isCustom || trigger[ event ]( coord );
if( isTrigger ){
// 加載圖片
elem.src = lazySrc;
if( o.fadeIn ){
$elem.hide().fadeIn();
}
// 移除緩存
$elem.removeData( dataName );
// 從DOM數(shù)組中移除該DOM
elems.splice( i--, 1 );
}
}
// 所有的圖片加載完后卸載觸發(fā)事件
if( !elems.length ){
if( triggerElem ){
triggerElem.unbind( event, fire );
}
else{
container.unbind( o.event, fire );
}
$( window ).unbind( 'resize', fire );
elems = null;
}
};
var fire = function( e ){
loader( $(this), e.type );
};
// 綁定事件
container = event === 'scroll' ? container : $( this );
container.bind( event, fire );
$( window ).bind( 'resize', fire );
// 初始化
loader();
return this;
};
})( jQuery );