 
                        <!doctype html>
<html lang="en">
<head>
  <meta charset="UTF-8" />
  <style>
*{list-style-type: none;}
#colcon li{ width: 50px; height: 50px; border:1px solid #ccc; float: left; margin:10px;line-height: 50px; background-color:#fcc;text-align: center;} 
</style>
<script>
window.onload=function (){
 var aUL=document.getElementById("colcon");
 var aLI=aUL.getElementsByTagName("li");
 aUL.onclick = function(ev){
     var ev = ev || window.event;
     var target = ev.target || ev.srcElement; 
    if(target.nodeName.toLowerCase == "li"){
        
        var newcolo = target.innerHTML;
        target.style.background = newcolo;
      };
     
   };
   
    }
</script>
</head>
<body>
<ul id="colcon">
  <li>#000</li>
  <li>#ccc</li>
  <li>#ddd</li>
</ul>
</body>
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toLowerCase后边加括号
这样就可以了,试着单步调试,用console.log()
target.nodeName.toLowerCase()
改成这个就可以了
楼上正解
toLowerCase(),你把后边的括号掉了。