HTML 5 input placeholder 属性如何完美兼任ie

$(document).ready(function () {
if ($.browser.msie)
$("input:text,input:password").each(function () {
var $placeholder = $(this).attr("placeholder");
var $width = $(this).css("width");
var $id = $(this).attr("id");
var $height = parseInt($(this).css("height")) + 6 + "px";
var $fontSize = $(this).css("font-size");
var $fontWeight = $(this).css("font-weight");
var $lineHeight = $height;
if ($(this).css("line-height") != "normal") {
$lineHeight = parseInt($(this).css("line-height")) + 6 + "px";
}
if ($placeholder != undefined) {
$(this).after("<span class=\"placeholder ph_" + $id + "\" style=\"width:" + $width + ";line-height:" + $lineHeight + ";height:" + $height + ";font-weight:" + $fontWeight + ";margin-left:-" + $width + ";font-size:" + $fontSize + "\">" + $placeholder + "</span>");
}
$(this).bind("keyup", function () {
if ($(this).val() == "") {
$(this).parent().find(".ph_" + $id).css("display", "inline-block");
}
else {
$(this).parent().find(".ph_" + $id).css("display", "none");
}
});
});
$(".placeholder").live("click", function () {
$(this).prev().focus();
});
});

<input id="n1" type="text" placeholder="我是提示内容正常" />

<input id="n2" type="text" placeholder="我是提示内容宽高" style="width:100px;height:100px;" />

<input id="n3" type="text" placeholder="我是提示内容我有其他样式" / style="width:300px;height:40px;font-weight:bold;">

<input id="n4" type="text" placeholder="还可以尝试下其他的" />

<style type="text/css">
.placeholder {display:inline-block;color:gray;vertical-align:top;overflow:hidden;}
</style>