兼容ie9及以下placeholder失效的问题；需要提前引入jquery

    function isPlaceholder() {
      var input = document.createElement('input');
      return 'placeholder' in input;
    }
    if (!isPlaceholder()) { //不支持placeholder 用jquery来完成
      $(document).ready(function () {
        if (!isPlaceholder()) {
          $("input").not("input[type='password']").each( //把input绑定事件 排除password框
            function () {
              if ($(this).val() == "" && $(this).attr("placeholder") != "") {
                $(this).val($(this).attr("placeholder"));
                $(this).focus(function () {
                  if ($(this).val() == $(this).attr("placeholder")) $(this).val("");
                });
                $(this).blur(function () {
                  if ($(this).val() == "") $(this).val($(this).attr("placeholder"));
                });
              }
            });
          //对password框的特殊处理1.创建一个text框 2获取焦点和失去焦点的时候切换
          $("input[type='password']").each(
            function () {
              var pwdField = $(this);
              var pwdVal = pwdField.attr('placeholder');
              pwdField.after('<input  class="login-input" type="text" value=' + pwdVal +
              ' autocomplete="off" />');
              var pwdPlaceholder = $(this).siblings('.login-input');
              pwdPlaceholder.show();
              pwdField.hide();

              pwdPlaceholder.focus(function () {
                pwdPlaceholder.hide();
                pwdField.show();
                pwdField.focus();
              });

              pwdField.blur(function () {
                if (pwdField.val() == '') {
                  pwdPlaceholder.show();
                  pwdField.hide();
                }
              });
            })
        }
      });
    }

转自：https://www.cnblogs.com/vonson/p/4970867.html