SOURCE

var a = "attachment; filename=content.txt";
var b = "attachment; filename*=UTF-8''filename.txt";
var d = 'attachment; filename="123.jpg"';

var s = "attachment; filename*=utf-8''%E9%97%A8%E5%BA%97%E5%95%86%E5%9C%88%E4%BF%A1%E6%81%AF1606468054558.xlsx";
var tt = /filename[^;\n]*=(UTF-\d['"]*)?((['"]).*?[.]$\2|[^;\n]*)?/gi
console.log(a.match(tt),'aaaaaa')
console.log(b.match(tt),'bbbb')
console.log(d.match(tt),'dddd')
console.log(s.match(tt),'sss')

console.log(tt.exec(d)[0])
// var testStr = "now test001 test002";  
// var re = /test(\d+)/ig;   
// var r = "";  
// while(r = re.exec(testStr)) {  
//     alert(r[0] + "  " + r[1]);  
// }