nested-ngfor.js

const abc = [[0,1,2],[0,1],[0],[0,1,2]];

function countIndex(a, k) {

    if (a === 0 && k === 0) {
      return 0;
    } else if (k !== 0) {
      return this.countIndex(a, k-1) + 1;
    } else {
      const totalItem = abc[a-1].length;
      return this.countIndex(a-1, totalItem-1) + 1
    }
}

for (let i=0; i<abc.length; i++) {
  for(let j=0; j<abc[i].length; j++) {
    
    console.log(countIndex(i,j));
    
  }
}