var todayDate = new Date().toISOString().split('T')[0];
document.getElementsByName("myDate")[0].setAttribute('min', todayDate);
$(".book_btn").click(function(){
var today = new Date();
var date = today.getFullYear()+'-'+("0" +(today.getMonth()+1)).slice(-2)+'-'+("0" + today.getDate()).slice(-2);
//alert(date);//("0" + this.getDate()).slice(-2)
document.getElementById("myDate").defaultValue =date;
});
input[type=date]::-webkit-inner-spin-button {
-webkit-appearance: none;
display: none;
<input type="date" name="myDate" value="" id="myDate" />