Discussion on: Daily Challenge #201 - Complete the Pattern

function pattern(len) {
  if(isNaN(len) || len <1 ) {
    console.log('');
    return;
  }
  console.log( Array.from({ length: len }).map((item, index)=>{
    return Array.from({ length: index+1 }).fill(index+1).join('');
  }).join('\n'));
}