/**
 *textarea 字数限制
 *obj textarea 
 * maxlength 限制的最大字数
 */
function textarealength(obj,maxlength){
    var v = $(obj).val();
    var l = v.length;
    if( l > maxlength){
        v = v.substring(0,maxlength);
        $(obj).val(v);
    }
    $(obj).parent().find(".textarea-length").text(v.length);
}

<style>
.textarea-numberbar{ position:absolute; right:20px; bottom:5px; z-index:1; margin-bottom:0}
</style>
<textarea name="desc" placeholder="请输入内容" class="layui-textarea" lay-verify="required"  onKeyUp="textarealength(this,150)"></textarea>
<p class="textarea-numberbar"><em class="textarea-length">0</em>/150</p>