今天看了下jquery图片延迟加载的方法。感觉不错,对用户体验这块挺好的,摘抄下来,方便自己以后学习。
这里主要用的一个开源的js——jquery.lazyload.js,下面附上这个js的源代码
[code lang="js"]
<pre>/*
* Lazy Load - jQuery plugin for lazy loading images
*
* Copyright (c) 2007-2012 Mika Tuupola
*
* Licensed under the MIT license:
* http://www.opensource.org/licenses/mit-license.php
*
* Project home:
* http://www.appelsiini.net/projects/lazyload
*
* Version: 1.8.3
*
*/
(function($, window, document, undefined) {
var $window = $(window);
$.fn.lazyload = function(options) {
var elements = this;
var $container;
var settings = {
threshold : 0,
failure_limit : 0,
event : "scroll",
effect : "show",
container : window,
data_attribute : "original",
skip_invisible : true,
appear : null,
load : null
};
function update() {
var counter = 0;
elements.each(function() {
var $this = $(this);
if (settings.skip_invisible && !$this.is(":visible")) {
return;
}
if ($.abovethetop(this, settings) ||
$.leftofbegin(this, settings)) {
/* Nothing. */
} else if (!$.belowthefold(this, settings) &&
!$.rightoffold(this, settings)) {
$this.trigger("appear");
/* if we found an image we'll load, reset the counter */
counter = 0;
} else {
if (++counter > settings.failure_limit) {
return false;
}
}
});
}
if(options) {
/* Maintain BC for a couple of versions. */
if (undefined !== options.failurelimit) {
options.failure_limit = options.failurelimit;
delete options.failurelimit;
}
if (undefined !== options.effectspeed) {
options.effect_speed = options.effectspeed;
delete options.effectspeed;
}
$.extend(settings, options);
}
/* Cache container as jQuery as object. */
$container = (settings.container === undefined ||
settings.container === window) ? $window : $(settings.container);
/* Fire one scroll event per scroll. Not one scroll event per image. */
if (0 === settings.event.indexOf("scroll")) {
$container.bind(settings.event, function(event) {
return update();
});
}
this.each(function() {
var self = this;
var $self = $(self);
self.loaded = false;
/* When appear is triggered load original image. */
$self.one("appear", function() {
if (!this.loaded) {
if (settings.appear) {
var elements_left = elements.length;
settings.appear.call(self, elements_left, settings);
}
$("<img />")
.bind("load", function() {
$self
.hide()
.attr("src", $self.data(settings.data_attribute))
[settings.effect](settings.effect_speed);
self.loaded = true;
/* Remove image from array so it is not looped next time. */
var temp = $.grep(elements, function(element) {
return !element.loaded;
});
elements = $(temp);
if (settings.load) {
var elements_left = elements.length;
settings.load.call(self, elements_left, settings);
}
})
.attr("src", $self.data(settings.data_attribute));
}
});
/* When wanted event is triggered load original image */
/* by triggering appear. */
if (0 !== settings.event.indexOf("scroll")) {
$self.bind(settings.event, function(event) {
if (!self.loaded) {
$self.trigger("appear");
}
});
}
});
/* Check if something appears when window is resized. */
$window.bind("resize", function(event) {
update();
});
/* With IOS5 force loading images when navigating with back button. */
/* Non optimal workaround. */
if ((/iphone|ipod|ipad.*os 5/gi).test(navigator.appVersion)) {
$window.bind("pageshow", function(event) {
if (event.originalEvent.persisted) {
elements.each(function() {
$(this).trigger("appear");
});
}
});
}
/* Force initial check if images should appear. */
$(window).load(function() {
update();
});
return this;
};
/* Convenience methods in jQuery namespace. */
/* Use as $.belowthefold(element, {threshold : 100, container : window}) */
$.belowthefold = function(element, settings) {
var fold;
if (settings.container === undefined || settings.container === window) {
fold = $window.height() + $window.scrollTop();
} else {
fold = $(settings.container).offset().top + $(settings.container).height();
}
return fold <= $(element).offset().top - settings.threshold;
};
$.rightoffold = function(element, settings) {
var fold;
if (settings.container === undefined || settings.container === window) {
fold = $window.width() + $window.scrollLeft();
} else {
fold = $(settings.container).offset().left + $(settings.container).width();
}
return fold <= $(element).offset().left - settings.threshold;
};
$.abovethetop = function(element, settings) {
var fold;
if (settings.container === undefined || settings.container === window) {
fold = $window.scrollTop();
} else {
fold = $(settings.container).offset().top;
}
return fold >= $(element).offset().top + settings.threshold + $(element).height();
};
$.leftofbegin = function(element, settings) {
var fold;
if (settings.container === undefined || settings.container === window) {
fold = $window.scrollLeft();
} else {
fold = $(settings.container).offset().left;
}
return fold >= $(element).offset().left + settings.threshold + $(element).width();
};
$.inviewport = function(element, settings) {
return !$.rightoffold(element, settings) && !$.leftofbegin(element, settings) &&
!$.belowthefold(element, settings) && !$.abovethetop(element, settings);
};
/* Custom selectors for your convenience. */
/* Use as $("img:below-the-fold").something() or */
/* $("img").filter(":below-the-fold").something() which is faster */
$.extend($.expr[':'], {
"below-the-fold" : function(a) { return $.belowthefold(a, {threshold : 0}); },
"above-the-top" : function(a) { return !$.belowthefold(a, {threshold : 0}); },
"right-of-screen": function(a) { return $.rightoffold(a, {threshold : 0}); },
"left-of-screen" : function(a) { return !$.rightoffold(a, {threshold : 0}); },
"in-viewport" : function(a) { return $.inviewport(a, {threshold : 0}); },
/* Maintain BC for couple of versions. */
"above-the-fold" : function(a) { return !$.belowthefold(a, {threshold : 0}); },
"right-of-fold" : function(a) { return $.rightoffold(a, {threshold : 0}); },
"left-of-fold" : function(a) { return !$.rightoffold(a, {threshold : 0}); }
});
})(jQuery, window, document);</pre>
[/code]
使用方法:
1.导入JS插件
<script src="jquery.js" type="text/javascript"></script>
<script src="jquery.lazyload.js" type="text/javascript"></script>
2.在你的页面中加入如下的javascr
ipt:
$("img").lazyload();
这将会使所有的图片都延迟加载。
当然插件还有几个配置项可供设置。
1.改变threshold
$(“img”).lazyload({ threshold : 200 });
把阀值设置成200 意思就是当图片没有看到之前先load 200像素。
2.当然了你也可以通过设置占位符图片和自定事件来触发加载图片事件
[code lang="js"]
$("img").lazyload({
placeholder : "img/grey.gif",
event : "click"
});
[/code]
3.可以通过定义effect 参数来定义一些图片显示效果
[code lang="js"]
$("img").lazyload({
placeholder : "img/grey.gif",
effect : "fadeIn"
});
[/code]
LazyLoad(延迟加载)技术不仅仅用在对网页中图片的延迟加载,对数据同样可以,Google Reader和Bing图片搜索就把
LazyLoad技术运用的淋漓尽致;
缺陷:
1.与Ajax技术的冲突;
2.图片的延迟加载,遇到高度特别高的图片,会出现停止加载的问题;
3.写代码不规范的同学要注意了,不管由于什么原因,如果您的页面中,img标签的height属性未定义,那么我建议您最好不要使用ImageLazyLoad
下面附上抄的代码,呵呵:
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head><meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>图片延迟加载-柯乐义</title>
<script type="text/javascript" src="http://keleyi.com/keleyi/pmedia/jquery-1.9.1.min.js"></script>
<script type="text/javascript" src="http://keleyi.com/keleyi/phtml/image/jquery.lazyload.js"></script>
</head>
<body>
jquery实现图片延迟加载效果
<a href="
http://keleyi.com/a/bjac/et551617.htm" target="_blank">原文</a><br />
<img src="
http://keleyi.com/keleyi/phtml/image/img/grey.gif" data-original="
http://keleyi.com/keleyi/phtml/image/img/bmw_m1_hood.jpg" width="765" height="574" alt="BMW M1 Hood keleyi.com" /><br />
<img src="
http://keleyi.com/keleyi/phtml/image/img/grey.gif" data-original="
http://keleyi.com/keleyi/phtml/image/img/bmw_m1_side.jpg" width="765" height="574" alt="BMW M1 Side keleyi.com" /><br />
<img src="
http://keleyi.com/keleyi/phtml/image/img/grey.gif" data-original="
http://keleyi.com/keleyi/phtml/image/img/viper_1.jpg" width="765" height="574" alt="Viper 1 keleyi.com" />
<img src="
http://keleyi.com/keleyi/phtml/image/img/grey.gif" data-original="
http://keleyi.com/keleyi/phtml/image/img/viper_corner.jpg" width="765" height="574" alt="Viper Corner keleyi.com" /><br />
<img src="
http://keleyi.com/keleyi/phtml/image/img/grey.gif" data-original="
http://keleyi.com/keleyi/phtml/image/img/bmw_m3_gt.jpg" width="765" height="574" alt="BMW M3 GT keleyi.com" />
<img src="
http://keleyi.com/keleyi/phtml/image/img/grey.gif" data-original="
http://keleyi.com/keleyi/phtml/image/img/corvette_pitstop.jpg" width="765" height="574" alt="Corvette Pitstop keleyi.com" />
<script type="text/javascript" charset="utf-8">
$(function () {
$("img").lazyload({
effect: "fadeIn"
});
});
</script>
</body>
</html>