자바스크립트 숫자에 천단위 추가

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>javascript 숫자포맷</title>
<script type="text/javascript">
function addThousandSeparator(number) {

    if( typeof number === "number" ) {
        let numArr = String(number).split(".");
        let returnNumber = numArr[0].toString().replace(/\B(?=(\d{3})+(?!\d))/g, ",");
        if( numArr[1] ) returnNumber += "."+numArr[1];

        return returnNumber;
    }
    else {
        return number;
    }

}// 사용 예시
const numberWithSeparator = addThousandSeparator(1234567.1234);
console.log(numberWithSeparator); // 출력: "1,234,567.1234567"
const numberWithSeparator1 = addThousandSeparator(.1234);
console.log(numberWithSeparator1);
const numberWithSeparator2 = addThousandSeparator(0.1234);
console.log(numberWithSeparator2);
const numberWithSeparator3 = addThousandSeparator(1212120);
console.log(numberWithSeparator3);
</script>
</head>
<body>
<ul><li>javascript 숫자포멧 : console.log 확인</li></ul>
</body>
</html>