Test your knowledge: JavaScript Loops

Review

1. Over an array, what is the difference between for...of and for...in?

   for...of hands the loop the element values, while for...in hands it the property names, which over an array arrive as strings like "0" and "1". Choose without flinching, the quick check says, and this is the flinch.
2. A search loop finds its match and hits break. What happens to the rest of the array?

   break leaves the loop entirely on the spot, so the elements after the match are never visited. That is the efficiency and the danger of it: it is also how you walk only as far as the answer.
3. When does a while loop beat a for?

   while is for repetition whose stopping is decided by a condition turning, not by a list running out. The lesson's while carried two facts, and stopped when either one gave out.
4. The final menu line in the lesson was never a loop at all. What said it in one call?

   map said the final line in one call, turning each item into its text and joining the results, no loop written. The array methods eat the loops whose bodies were only ever a transformation.
5. Why does the lesson warn against for...in over arrays specifically?

   for...in walks property names, so the index arrives as a string and any inherited properties come along for the walk, which makes arithmetic and early exits both treacherous. for...of walks the elements themselves and none of this can happen.