Is this what do you want?

var x=[1,2,3,4];
var z=["1z","2z","3z","4z","5z","6z"];
var y=["1y","2y"];
for(i=0;i<Math.max(x.length, y.length, z.length);i++)
{
  console.log(x[i] ? x[i]:"");
  console.log(y[i] ? y[i]:"");
  console.log(z[i] ? z[i]:"");
}