javascript 加减1

function plus_one(ths){
        var offsetTop = -10;
        var offsetLeft = 20;
        var fontSize = 24;
        var opacity = 1;
        var tag = document.createElement('i');
        tag.innerText = "+1";
        tag.style.position = 'absolute';
        tag.style.top = offsetTop + 'px';
        tag.style.left = offsetLeft + 'px';
        tag.style.fontSize = fontSize + "px";
        tag.style.color = "#5cb85c";
        $(ths).append(tag);
        var addInterval = setInterval(function(){
                fontSize += 5;
                offsetTop -= 15;
                offsetLeft += 5;
                opacity -= 0.1;
                tag.style.top = offsetTop+ 'px';
                tag.style.left = offsetLeft+ 'px';
                tag.style.fontSize = fontSize + 'px';
                tag.style.opacity = opacity;
            if(opacity <= 0.5){
                tag.remove();
                clearInterval(addInterval);
            }
        },40)
    }

function reduce_one(ths){
        var offsetTop = -10;
        var offsetLeft = 20;
        var fontSize = 24;
        var opacity = 1;
        var tag = document.createElement('i');
        tag.innerText = "-1";
        tag.style.position = 'absolute';
        tag.style.top = offsetTop + 'px';
        tag.style.left = offsetLeft + 'px';
        tag.style.fontSize = fontSize + "px";
        tag.style.color = "#787878";
        $(ths).append(tag);
        var addInterval = setInterval(function(){
                fontSize += 5;
                offsetTop -= 15;
                offsetLeft += 5 ;
                opacity -= 0.1;
                tag.style.top = offsetTop+ 'px';
                tag.style.left = offsetLeft+ 'px';
                tag.style.fontSize = fontSize + 'px';
                tag.style.opacity = opacity;
            if(opacity <= 0.5){
                tag.remove();
                clearInterval(addInterval);
            }
        },40)
      }