兼容不支持placeholder的浏览器

placeholder.css

.placeholder{color:#A2A2A2;}
::-webkit-input-placeholder { /* WebKit browsers */
    color:#A2A2A2;
}
:-moz-placeholder { /* Mozilla Firefox 4 to 18 */
    color:#A2A2A2;
}
::-moz-placeholder { /* Mozilla Firefox 19+ */
    color:#A2A2A2;
}
:-ms-input-placeholder { /* Internet Explorer 10+ */
    color:#A2A2A2;
}

placeholder.js

var supportsPlaceholder = 'placeholder' in document.createElement('input');
$('[placeholder]').each(function () {
	if (!supportsPlaceholder) {
		var self = $(this);

		self.val(self.attr('placeholder')).addClass('placeholder');
		
		self.focus(function(){
			if (self.val() == self.attr('placeholder')) {
				self.val('').removeClass('placeholder');
			}
		});

		self.blur(function(){
			if (self.val() == '') {
				self.val(self.attr('placeholder')).addClass('placeholder');
			}
		});
	}	
});