Function to remove Vietnamese's diacritic marks.

bodauTiengViet.js

const bodauTiengViet = str => {
    str = str.toLowerCase();
    str = str.replace(/à|á|ạ|ả|ã|â|ầ|ấ|ậ|ẩ|ẫ|ă|ằ|ắ|ặ|ẳ|ẵ/g, 'a');
    str = str.replace(/è|é|ẹ|ẻ|ẽ|ê|ề|ế|ệ|ể|ễ/g, 'e');
    str = str.replace(/ì|í|ị|ỉ|ĩ/g, 'i');
    str = str.replace(/ò|ó|ọ|ỏ|õ|ô|ồ|ố|ộ|ổ|ỗ|ơ|ờ|ớ|ợ|ở|ỡ/g, 'o');
    str = str.replace(/ù|ú|ụ|ủ|ũ|ư|ừ|ứ|ự|ử|ữ/g, 'u');
    str = str.replace(/ỳ|ý|ỵ|ỷ|ỹ/g, 'y');
    str = str.replace(/đ/g, 'd');
    // 2 lines below to replace spaces to '-', uncomment if you need.
    // str = str.replace(/\W+/g, ' ');
    // str = str.replace(/\s/g, '-');
    return str;
}