Chapter II: The for/of loop

A new kind of loop

In the first chapter, we learned about tradeoffs between pull and push mode for consuming collections. However, ES6 introduces a new way of looping that we failed to take into account: the for/of loop.

Solving the pull/push conundrum

Compare these two ways of looping an array:

for (var i=0; i<arr.length; i++) {
  var value = arr[i];

for (var value of arr) {

Unlike push mode, for/of retains all the language-level powers of a loop:

Unlike pull mode, for/of avoids problems with other kinds of loops:

In other words, for/of retains the benefits of pull mode, while also gaining the benefits of push mode.

What makes something for/of-able?

Above, we used for/of to loop an array, but it raises the question: what makes something for/of-able? Do only arrays have this ability, or could our binary search tree from the last chapter also be for/of'd? That's where ES6 iterators come in, and it's the topic of the next chapter.

Next: Chapter III: Iterators →

Copyright © 2016 by Greg Reimer (github, twitter). Submit issues to the GitHub issues page.