<textarea cols="20" rows="10" id="dome1">
			
</textarea>
<h2 id="dome2">剩余(100)个字符</h2>
<br />
<button onclick="func1()">统计个数</button>
<div id="dome"></div>

       js：操作      

function func1(){
var x = document.getElementById("dome1").value;
var upCount = 0;
var lowCount = 0;
var otherCount = 0;
for (var i=0;i<x.length;i++) {
var c = x.charAt(i);
if (c >= 'a' && c <='z') {
lowCount++;
} else if(c >= 'A' && c <='Z'){
upCount++;
}else{
otherCount++;
}
}
var zifu =Number(x.length);
var da = 120 - zifu;
document.getElementById("dome2").innerHTML="剩余("+da+")个字符";
document.getElementById("dome").innerHTML="大写字母个数为:"+upCount+",小写字母个数为"+lowCount+",其他字符:"+otherCount;
}