jquery.lazyload.js源码欣赏
官方Github地址：https://github.com/tuupola/jquery_lazyload/
1.9.1版本 从.min.js中还原出 无注释
(function($) {
$.fn.lazyload = function(options) {
var settings = {
threshold: 0,
failurelimit: 0,
event: "scroll",
effect: "show",
container: window
};
if (options) {
$.extend(settings, options)
}
var elements = this;
if ("scroll" == settings.event) {
$(settings.container).bind("scroll", function(event) {
var counter = 0;
elements.each(function() {
if (!$.belowthefold(this, settings) && !$.rightoffold(this, settings)) {
$(this).trigger("appear")
} else {
if (counter++ > settings.failurelimit) {
return false
}
}
});
var temp = $.grep(elements, function(element) {
return !element.loaded
});
elements = $(temp)
})
}
return this.each(function() {
var self = this;
$(self).attr("original", $(self).attr("src"));
if ("scroll" != settings.event || $.belowthefold(self, settings) || $.rightoffold(self, settings)) {
if (settings.placeholder) {
$(self).attr("src", settings.placeholder)
} else {
$(self).removeAttr("src")
}
self.loaded = false
} else {
self.loaded = true
}
$(self).one("appear", function() {
if (!this.loaded) {
$("<img />").bind("load", function() {
$(self).hide().attr("src", $(self).attr("original"))[settings.effect](settings.effectspeed);
self.loaded = true
}).attr("src", $(self).attr("original"))
}
});
if ("scroll" != settings.event) {
$(self).bind(settings.event, function(event) {
if (!self.loaded) {
$(self).trigger("appear")
}
})
}
})
};
$.belowthefold = function(element, settings) {
if (settings.container === undefined || settings.container === window) {
var fold = $(window).height() + $(window).scrollTop()
} else {
var fold = $(settings.container).offset().top + $(settings.container).height()
}
return fold <= $(element).offset().top - settings.threshold
};
$.rightoffold = function(element, settings) {
if (settings.container === undefined || settings.container === window) {
var fold = $(window).width() + $(window).scrollLeft()
} else {
var fold = $(settings.container).offset().left + $(settings.container).width()
}
return fold <= $(element).offset().left - settings.threshold
};
$.extend($.expr[':'], {
"below-the-fold": "$.belowthefold(a, {threshold : 0, container: window})",
"above-the-fold": "!$.belowthefold(a, {threshold : 0, container: window})",
"right-of-fold": "$.rightoffold(a, {threshold : 0, container: window})",
"left-of-fold": "!$.rightoffold(a, {threshold : 0, container: window})"
})
})(jQuery);
1.9.3最新版 有注释
/*
* Lazy Load - jQuery plugin for lazy loading images
*
* Copyright (c) 2007-2013 Mika Tuupola
*
* Licensed under the MIT license:
* http://www.opensource.org/licenses/mit-license.php
*
* Project home:
* http://www.appelsiini.net/projects/lazyload
*
* Version: 1.9.3
*
*/
(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,
placeholder : "data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAAEAAAABCAYAAAAfFcSJAAAAAXNSR0IArs4c6QAAAARnQU1BAACxjwv8YQUAAAAJcEhZcwAADsQAAA7EAZUrDhsAAAANSURBVBhXYzh8+PB/AAffA0nNPuCLAAAAAElFTkSuQmCC"
};
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() {
return update();
});
}
this.each(function() {
var self = this;
var $self = $(self);
self.loaded = false;
/* If no src attribute given use data:uri. */
if ($self.attr("src") === undefined || $self.attr("src") === false) {
if ($self.is("img")) {
$self.attr("src", settings.placeholder);
}
}
/* 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() {
var original = $self.attr("data-" + settings.data_attribute);
$self.hide();
if ($self.is("img")) {
$self.attr("src", original);
} else {
$self.css("background-image", "url('" + original + "')");
}
$self[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.attr("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() {
if (!self.loaded) {
$self.trigger("appear");
}
});
}
});
/* Check if something appears when window is resized. */
$window.bind("resize", function() {
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 && event.originalEvent.persisted) {
elements.each(function() {
$(this).trigger("appear");
});
}
});
}
/* Force initial check if images should appear. */
$(document).ready(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.innerHeight ? window.innerHeight : $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);
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