关于backtop.js文件判断浏览器屏幕滚动条代码
老师可以发下源码吗？照着打的还是会出现问题，当滚动一屏时返回顶部的按钮显示不出来，只有刷新可以显示，哪里错了呢？
define(['jquery','scrollto'],function($,scrollto){
function BackTop(el,opts){
this.opts=$.extend({},BackTop.DEFAULTS,opts);
this.$el=$(el);
this.scroll=new scrollto.ScrollTo({
dest:0,
speed:this.opts.speed
});
this._checkPosition();
if(this.opts.mode =='move'){
this.$el.on('click',$.proxy(this._move,this));
}else{
this.$el.on('click',$.proxy(this._go,this));
}
$(window).on('scroll',$.proxy(this._checkPosition.this));
}
BackTop.DEFAULTS={
mode:'move',
pos:$(window).height(),
speed:800
}
BackTop.prototype._move=function(){
this.scroll.move();
}
BackTop.prototype._go=function(){
this.scroll.go();
}
BackTop.prototype._checkPosition = function() {
var $el=this.$el;
if ($(window).scrollTop() > this.opts.pos){
//alert(this.opts.pos)
// console.log($(window).scrollTop)
this.$el.fadeIn()
}else{
this.$el.fadeOut();
}
};
$.fn.extend({
backtop:function(opts){
return this.each(function(){
new BackTop(this,opts)
})
}
})
return {
BackTop:BackTop
};
})
