index.md

title	tags	order	date	answers
Reduce Object	reduce array	39	2019-09-22	hello // correct eohll Order not guaranteed

Consider the following code block. What gets logged?

const scrambled = { 2: "e", 5: "o", 1: "h", 4: "l", 3: "l" };

const result = Object
  .values(scrambled)
  .reduce((agg, el) => agg + el, "");

console.log(result);

Object.values iterates through enumerable integer keys starting from 0 in sequential order. This is the reason why the letters appear to sort themselves correctly. (Very recently, it used to be the case that Object.values did not guarantee the order of iteration over properties, but this is no longer the case, as of December 2019.)

The reduce method then takes two arguments: a reducer function and an initial value.

• In this case, our reducer function is (agg, el) => agg + el and our initial value is "".
• In the reducer function, agg is the aggregator (which starts at the initial value) and el is an element in the array being iterated over. In this case, as we iterate through the array, we add the current el to the aggregated value.
• If our array was ['a', 'b', 'c'], then the aggregator would be a after the first iteration, ab the second time, and finally would return abc.