<div class="font-limit">
					<input type="text" id="username" autoComplete='off' maxlength="17" onkeyUp="textLimitCheck(this, 17);" placeholder="请输入17位车架号">
					<span class="js_limit">
					    <em id="messageCount">0</em>/<span>17</span>
					</span>
					<span style="margin-left: 2%;"><img src="img/ercode.png" style="width: .17rem;"></span>
				</div>
//文字限制
		function textLimitCheck(thisArea, maxLength){
		    if (thisArea.value.length > maxLength){
		        alert(maxLength + ' 个字限制. \r超出的将自动去除.');   
		        thisArea.value = thisArea.value.substring(0, 17); 
		        thisArea.focus();
		    }    /*回写span的值，当前填写文字的数量*/  
		    messageCount.innerText = thisArea.value.length; 
		}