bluevivid

function mapDiagonal(arr){

    var row_mapper = Array.from({length: arr.length}, (v, i) => i),
        col_mapper = Array.from({length: arr[0].length}, (v, i) => i),
        _mapper = row_mapper.map(val => col_mapper.map(_val => [val,_val]));

        _mapper = _mapper.reduce((acc,cur)=>{
            acc = acc.concat(cur)
            return acc;
          }, [])