bash-str.js

const assert = require('assert')

const solution = (str) => {
  const checkSubs = (s, oldResults=[]) => {
    let start = s.indexOf('{')
    let end = s.indexOf('}', start+1)
    // console.log('yo', s, start, end,s.substring(end+1, s.length))
    if (start<0 && end <0) {
      for (let i = 0; i<oldResults.length; i++) {
        oldResults[i] += s
      }
      return oldResults
    } else {
      let pattern = s.substring(start+1, end).split(',')
      let results = []
      for (let i=0; i<pattern.length; i++) {
        if (oldResults.length == 0) results.push(s.substring(0, start)+pattern[i])
        else for (let j=0; j<oldResults.length; j++) {
          results.push(oldResults[j] + s.substring(0, start)+pattern[i])
        }        
      }
      // console.log(pattern, results)
      return checkSubs(s.substring(end+1, s.length), results)
    }
  }
  return checkSubs(str, [])
}

assert.deepEqual(['hello_1_A', 'hello_2_A', 'hello_3_A', 'hello_1_B', 'hello_2_B', 'hello_3_B'], solution('hello_{1,2,3}_{A,B}'))
assert.deepEqual(['1@m!', '2@m!', '1@l!', '2@l!', '1@m!', '2@m!'], solution('{1,2}@{m,l,m}!'))