web性能优化之- js自定义函数延迟执行 jquery插件
今天碰到一个很奇快的需求，大致如下：html页面有很多div容器，每个div容器的数据都是通过ajax请求来处理的。一般情况处理ajax请都在windows的load事件中，由于页面的div容器太多造成windows的load事件中ajax请求太多；所以我们只需要处理那些在浏览器中看得见的div容器。假如我们现在有10个div容器，每个屏幕刚好显示1个div容器，如果我们放到windows的load事件中，那么刚开始就有10个ajax请求。其实用户可能根本不会看到后面几个div容器，所以我们通过这个插件来延迟这些ajax的请求，刚加载页面有1个或2个ajax请求，当滚动条滚到相应div的时候，div再发起ajax请求。
jquery.lazyevent.js插件源代码:
(function ($, window) {
var $window = $(window);
$.fn.lazyevent = function (options) {
var elements = this;
var settings = {
threshold: 0,
event: "scroll",
container: window,
skip_invisible: true,
fn: null,
data: null
};
function update() {
var counter = 0;
elements.each(function () {
var $this = $(this);
if (settings.skip_invisible && !$this.is(":visible")) {
return;
}
/* if (!belowthefold(this, settings) && !rightoffold(this, settings)) {
$this.trigger("fire");
}*/
if (inviewport(this, settings)) {
$this.trigger("fire");
}
});
}
if (options) {
$.extend(settings, options);
}
var $container = (settings.container === undefined || settings.container === window) ? $window : $(settings.container);
if (0 === settings.event.indexOf("scroll")) {
$container.bind(settings.event, function (event) { return update(); });
}
this.each(function () {
var self = this;
var $self = $(self);
self.fired = false;
$self.one("fire", function () {
if (!this.fired) {
if (settings.fn) {
settings.fn.call(self, settings.data);
}
self.fired = true;
var temp = $.grep(elements, function (element) { return !element.fired; });
elements = $(temp);
}
});
if (0 !== settings.event.indexOf("scroll")) {
$self.bind(settings.event, function (event) {
if (!self.fired) {
$self.trigger("fire");
}
});
}
});
$window.bind("resize", function (event) {
update();
});
var belowthefold = function (element, settings) {
var fold;
if (settings.container === undefined || settings.container === window) {
fold = $window.height() + $window.scrollTop();
} else {
fold = $container.offset().top + $container.height();
}
return fold <= $(element).offset().top - settings.threshold;
};
var rightoffold = function (element, settings) {
var fold;
if (settings.container === undefined || settings.container === window) {
fold = $window.width() + $window.scrollLeft();
} else {
fold = $container.offset().left + $container.width();
}
return fold <= $(element).offset().left - settings.threshold;
};
var abovethetop = function (element, settings) {
var fold;
if (settings.container === undefined || settings.container === window) {
fold = $window.scrollTop();
} else {
fold = $container.offset().top;
}
return fold >= $(element).offset().top + settings.threshold + $(element).height();
};
var leftofbegin = function (element, settings) {
var fold;
if (settings.container === undefined || settings.container === window) {
fold = $window.scrollLeft();
} else {
fold = $container.offset().left;
}
return fold >= $(element).offset().left + settings.threshold + $(element).width();
};
var inviewport = function (element, settings) {
return !abovethetop(element, settings) && !leftofbegin(element, settings) &&
!belowthefold(element, settings) && !rightoffold(element, settings);
};
update();
return this;
};
})(jQuery, window);
jquery.lazyevent..min.js代码：
(function(a,c){var b=a(c);a.fn.lazyevent=function(j){var g=this;var l={threshold:0,event:"scroll",container:c,skip_invisible:true,fn:null,data:null};function m(){var n=0;g.each(function(){var o=a(this);if(l.skip_invisible&&!o.is(":visible")){return}if(h(this,l)){o.trigger("fire")}})}if(j){a.extend(l,j)}var d=(l.container===undefined||l.container===c)?b:a(l.container);if(0===l.event.indexOf("scroll")){d.bind(l.event,function(n){return m()})}this.each(function(){var o=this;var n=a(o);o.fired=false;n.one("fire",function(){if(!this.fired){if(l.fn){l.fn.call(o,l.data)}o.fired=true;var p=a.grep(g,function(q){return !q.fired});g=a(p)}});if(0!==l.event.indexOf("scroll")){n.bind(l.event,function(p){if(!o.fired){n.trigger("fire")}})}});b.bind("resize",function(n){m()});var f=function(n,p){var o;if(p.container===undefined||p.container===c){o=b.height()+b.scrollTop()}else{o=d.offset().top+d.height()}return o<=a(n).offset().top-p.threshold};var k=function(n,p){var o;if(p.container===undefined||p.container===c){o=b.width()+b.scrollLeft()}else{o=d.offset().left+d.width()}return o<=a(n).offset().left-p.threshold};var e=function(n,p){var o;if(p.container===undefined||p.container===c){o=b.scrollTop()}else{o=d.offset().top}return o>=a(n).offset().top+p.threshold+a(n).height()};var i=function(n,p){var o;if(p.container===undefined||p.container===c){o=b.scrollLeft()}else{o=d.offset().left}return o>=a(n).offset().left+p.threshold+a(n).width()};var h=function(n,o){return !e(n,o)&&!i(n,o)&&!f(n,o)&&!k(n,o)};m();return this}})(jQuery,window);
html调用代码：
<!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>
<title>lazyevent</title>
<script type="text/javascript" src="Scripts/jquery-1.7.js"></script>
<script type="text/javascript" src="Scripts/jquery.lazyevent.js"></script>
<style type="text/css">
/* .test
{
height: 500px;
display: inline-block;
width: 4000px;
}
.test div
{
float: left;
}
*/.test div
{
width: 500px;
height: 500px;
}
</style>
</head>
<body>
<div style="height: 200px">
</div>
<div class="test">
<div style="background-color: Green">
Green</div>
<div style="background-color: Lime">
Lime</div>
<div style="background-color: Maroon; display:none">
Maroon</div>
<div style="background-color: Olive">
Olive</div>
<div style="background-color: Red; display: none">
Red</div>
<div style="background-color: ButtonFace">
ButtonFace</div>
<div style="background-color: Aqua">
Aqua</div>
<div style="background-color: AppWorkspace">
AppWorkspace</div>
</div>
<script type="text/javascript">
$(function () {
$(".test div").lazyevent({
data: "hello word",
fn: function (data) {
var html = $(this).html();
alert(data + ":" + html);
}
});
});
</script>
</body>
</html>