前端优化：BigRender

var winHeight = document.documentElement.clientHeight;
var sum = 0;
var count = 0;
var flash = new Array();

// ‘class’ 是textarea父节点的类；’textarea’ 是textarea标签的类；’threshold’是距离进入屏幕还有150像素就开始渲染；’remove’是否删除textarea标签
options = $.extend({
‘class’ : ‘.br-warp’,
‘textarea’ : ‘.br-rendered’,
‘threshold’ : 150,
‘remove’ : true,
},opts);

$brenders = $(options.class);
// 渲染首屏的内容
initBigrender();
// 绑定滚动条事件
scrollDisplay();

// 函数定义
function initBigrender(){
$brenders.each(function(n,object){
sum++;
if(isRender($(this))){
display($(this));
count++;
flash[n] = true;
}else{
flash[n] = false;
}
});
}

// 判断时候需要渲染
function isRender(object){
offsetTop = object.offset().top;
ojh = object.outerHeight(true);
st = Math.max(document.body.scrollTop || document.documentElement.scrollTop);

if(offsetTop+ojh+options.threshold >= st && offsetTop-options.threshold < (st+winHeight)){
return true;
}else return false;

}

// 渲染textarea内的html代码
function display(object){
$display = object.find(options.textarea).eq(0);
if(options.remove){
object.append($display.val());
$display.remove();
}else{
object.append($display.val());
}
}

// 屏幕绑定滚动条事件，当待渲染的内容进入可视屏幕就触发isRender函数
function scrollDisplay(){
$(window).scroll(function(event) {
event.preventDefault();
if(count < sum){
$brenders.each(function(n,object){
if(flash[n] == false){
if(isRender($(this))){
display($(this));
count++;
flash[n] = true;
}else{
flash[n] = false;
}
}
});
}
});
}
};
})(jQuery);