Click back to the top JS

   gotopping() {
    
            clearInterval(this.timers);
            this.timers = setInterval(() => {
    
                let curHeight = document.documentElement.scrollTop || document.body.scrollTop;
                var now = curHeight;
                //  Speed  = 0 -  The height of the roll   except  7  It's a negative number 
                var speed = (0 - now) / 7;
                //  Whether the speed value is greater than 0  Greater than 0  Rounding up    Less than 0  Rounding down 
                speed = speed > 0 ? Math.ceil(speed) : Math.floor(speed);
                //  Here, judge whether the value of the last scroll to the top is 0  by 0  It means that you have reached the top and don't need to scroll up   Clear timer   Hide the scroll button 
                if (curHeight == 0) {
    
                    clearInterval(this.timers);
                    this.toTop = false;
                }
                //  Scroll up the scroll bar    Even if the value is negative    Finally, the value obtained is  0 
                document.documentElement.scrollTop = curHeight + speed;
                document.body.scrollTop = curHeight + speed;
                //  Stop scrolling   Why not 
                this.stop = false;
            }, 30);
        },
        //  Listen to the function when scrolling up 
        needToTop() {
    
            //  compatible ie and chrome Writing   ie Only body attribute   chrome Only docmengElement attribute 
            let curHeight = document.documentElement.scrollTop || document.body.scrollTop;
            //  Determine whether there is a scroll bar   If so, the back to top button is displayed   Otherwise hide 
            if (curHeight == 0) {
    
                this.toTop = false;
            } else {
    
                this.toTop = true;
            }
            //  If there is a drop-down behavior    Just clear the timer   
            if (this.stop) {
    
                clearInterval(this.timers);
            }
            this.stop = true;
        },