function Toast(msg,duration){

      duration=isNaN(duration)?3000:duration;

      var m = document.createElement('div');

      m.innerHTML = msg;

      m.style.cssText="max-width:60%;min-width: 150px;padding:0 14px;height: 40px;color: rgb(255, 255, 255);line-height: 40px;text-align: center;border-radius: 4px;position: fixed;top: 50%;left: 50%;transform: translate(-50%, -50%);z-index: 999999;background: rgba(0, 0, 0,.7);font-size: 16px;";

      document.body.appendChild(m);

      setTimeout(function() {

        var d = 0.5;

        m.style.webkitTransition = '-webkit-transform ' + d + 's ease-in, opacity ' + d + 's ease-in';

        m.style.opacity = '0';

        setTimeout(function() { document.body.removeChild(m) }, d * 1000);

      }, duration);

    }

Toast('这是一个弹框',2000)