Want to create a custom button

Frappe Framework Customization
6

Here is my script :

frappe.ui.form.on("Times", {


	check_in_btn: function(frm){
		check_in_time(frm);
	},
	check_out_btn: function(frm){
		check_out_time(frm);
	}



});

var check_in_time = function(frm)
{
		frm.set_value("check_in", frappe.datetime.now_time());
		frm.set_value("check_in_date", frappe.datetime.get_today());
}
var check_out_time = function(frm)
{
		frm.set_value("check_out", frappe.datetime.now_time());
		frm.set_value("check_out_date", frappe.datetime.get_today());
		var start = frm.doc.check_in.split(":");
		var end = frm.doc.check_out.split(":");
		var date1 = new Date(2000, 0, 1,  start[0], start[1]); 
		var date2 = new Date(2000, 0, 1, end[0], end[1]); 

		if (date2 < date1) {
			date2.setDate(date2.getDate() + 1);
		}

		var diff = date2 - date1;
		var msec = diff;
		var hh = Math.floor(msec / 1000 / 60 / 60);
		msec -= hh * 1000 * 60 * 60;
		var mm = Math.floor(msec / 1000 / 60);
		msec -= mm * 1000 * 60;
		var ss = Math.floor(msec / 1000);
		msec -= ss * 1000;
		
		frm.set_value("total", hh+":"+mm+":"+ss);
}