在getElementById内使用变量时遇到麻烦

我想转换这些代码：

if(slidedLcount == 0){
        document.getElementById("incredable__offers__examples__item_1").style.cssText = "animation-name: SlideL_first;";
        document.getElementById("incredable__offers__examples__item_2").style.cssText = "animation-name: SlideL_first;";
        document.getElementById("incredable__offers__examples__item_3").style.cssText = "animation-name: SlideL_first;";
        document.getElementById("incredable__offers__examples__item_4").style.cssText = "animation-name: SlideL_first;";
        document.getElementById("incredable__offers__examples__item_5").style.cssText = "animation-name: SlideL_first;";
        document.getElementById("incredable__offers__examples__item_6").style.cssText = "animation-name: SlideL_first;";
        document.getElementById("incredable__offers__examples__item_7").style.cssText = "animation-name: SlideL_first;";
        document.getElementById("incredable__offers__examples__item_8").style.cssText = "animation-name: SlideL_first;";
        document.getElementById("incredable__offers__examples__item_9").style.cssText = "animation-name: SlideL_first;";
        document.getElementById("incredable__offers__examples__item_10").style.cssText = "animation-name: SlideL_first;";
        document.getElementById("incredable__offers__examples__arrow__r").classList.remove("grayedout");
    }

这些使它变得更容易，因为会多次使用它：

if(slidedLcount == 0){
        var x = "0";
        var y = "incredable__offers__examples__item_"
        while(x<10){
            var z = y+x;
            document.getElementById(z).style.cssText = "animation-name: SlideL_first;";
            x = (x*1)+1;
        }
        document.getElementById("incredable__offers__examples__arrow__r").classList.remove("grayedout");
    }

但是得到这个错误

mainscript.js：67未捕获的TypeError：无法读取null的属性“样式”