jquery 图片预加载，先模糊后清晰(源代码区)

摘要: Lazy Load 是一个用 JavaScript 编写的 jQuery 插件. 它可以延迟加载长页面中的图片. 在浏览器可视区域外的图片不会被载入, 直到用户将页面滚动到它们所在的位置. 这与图片预加载的处理方式正好是相反的.

/*
* 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:  1.8.0
*
*/
(function($, window) {
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) ||
$.leftofbegin(this,&
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nbsp;settings)) {
/* Nothing. */
} else if (!$.belowthefold(this, settings) &&
!$.rightoffold(this, settings)) {
$this.trigger("appear");
} 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();
});

/* Force initial check if images should appear. */
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();
};

$.inviewport = function(element, settings) {
return !$.rightofscreen(element, settings) && !$.leftofscreen(element, settings) &&
!$.belowthefold(element, settings) && !$.abovethetop(element, settings);
};

/* Custom selectors for your convenience.   */
/* Use as $("img:below-the-fold").something() */
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$.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);

使用教程看这里