Scanner

scanner.js

class Scanner {
  constructor(array) {
    this.idx   = 0;
    this.array = array;
    this.stack = [this];
    this.prev  = null;
  }
 
  next() {
    const scanner = this.stack[this.stack.length - 1];

    if (!scanner) {
      return null;
    }
   
    const next = scanner.array[scanner.idx];
   
    scanner.idx++;
   
    if (Array.isArray(next)) {
      this.stack.push(new Scanner(next));
      return this.next();
    } else if (!next) {
      this.stack.pop();
      return this.next();
    } else {
      const prev = this.prev;
      this.prev = next;
      return [prev, next];
    }
  }
}

const array   = [1, 2, [3, [4], 5], 6, [7, [8, 9]], 10];
const scanner = new Scanner(array);

let pair;
while ((pair = scanner.next()) !== null) {
  console.log('pair', pair);
  i++;
}

console.log('Done!');