定义BackTop，引用scrollto
define([‘jquery‘,‘scrollto‘],function($,scrollto){
function BackTop(el,opts){//定义构造函数
this.opts=$.extend({},BackTop.DEFAULTS,opts);
this.$el=$(el);
this.scroll=new scroll.ScrollTo({
dest:0,
speed:this.opts.speed
})
this._checkPosition();
$(window).on(‘scroll‘,$.proxy(this._checkPosition,this));
if(this.opts.mode==‘move‘){
this.$el.on(‘click‘,$.proxy(this._move,this));
}else{
this.$el.on(‘click‘,$.proxy(this._go,this));
}
}
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){
$el.fadeIn();
}else{
$el.fadeOut();
}
};
return{
BackTop:BackTop;
}
})