<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>Document</title>
</head>
<body>
<script>
function isYear(year){
return year % 4 == 0 && year % 100 !== 0 || year % 400 == 0;
}
function getDay(year, month, day){
var days = day;
if(month == 1){
return days;
}else{
var arr = [31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31];
for(var i=0; i<month-1; i++ ) {
days += arr[i]
}
}
if (isYear(year) && month > 2){
days++;
}
return days;
}
console.log(getDay(2020, 8, 12));
</script>
</body>
</html>