'aa_bb_cc'.replace('_', ',').split(',');
//["aa", "bb_cc"]

function trans (str) {
    let r = str.split('_')
    return [r[0], r.slice(1).join('_')]
}
trans('aa_bb_cc')

let str = 'aa_bb_cc';
let arr = str.split('_',1);
str = str.slice(str.indexOf('_')+1);
arr.push(str);
console.log(arr);

var s = 'aa_bb_cc';
var index = s.indexOf('_');
var rs = [s.slice(0, index), s.slice(index+1)];
console.log(rs);