解决placeholder不兼容问题

<script>

$(function(){

if(!placeholderSupport()){ // 判断浏览器是否支持 placeholder

$('[placeholder]').focus(function() {

var input = $(this);

if (input.val() == input.attr('placeholder')) {

input.val('');

input.removeClass('placeholder');

}

}).blur(function() {

var input = $(this);

if (input.val() == '' || input.val() == input.attr('placeholder')) {

input.addClass('placeholder');

input.val(input.attr('placeholder'));

}

}).blur();

};

})

function placeholderSupport() {

return 'placeholder' in document.createElement('input');

}

</script>