SOURCE

var aa = "sectionData_file_ldfd_0499";
var bb = "sectionData_file_ldfd_0419_0";

var cc = 'sectionData_file_ldfd_0404_1';
console.log(aa.length);

console.log(aa.substr(22,4)); 

console.log(bb.substr(22,4));

console.log(cc.substr(27,1));