buildTriangle.js

Build a triangle with loops

function buildTriangle(numLines) {
  var linesArray = [];
  var iterations = numLines;
  
  if (numLines < 1 ) {
    return alert("Try a bigger number!")
  }
  
  for (var line = 1; line <= iterations; line++) {    //start @ 1 instead of zero to avoid empty first index string
  linesArray.push("#".repeat(line) + "\n");
  }
  return console.log(linesArray.join(""));
}

Try this - I think it makes it more readable: https://jsfiddle.net/q9xywy8m/5/