Day 4 of JS30 challenge, today I worked with various methods on array (I knew most of them beforehand) but I learned two cool things today.

The key concepts I learned from today’s challenge were:

  • Converting iterables to array in JS.
  • Displaying array of objects nicely formatted in console.

Converting iterables to array in JS

As you might have observed that document.querySelectorAll doesn’t return us an actual Array but instead it returns us what is called as a NodeList. Consequently NodeList doesn’t have all the methods that an Array does (like map, filter, reduce etc).

NodeList is an example of what we call as “iterable” in JS. So whenever working with iterables we tend to prefer to convert them to an actual Array so that we have more options to work with.

I already knew of one way to convert them:

const anyIterable = document.querySelectorAll('a');
const convertedArray = Array.from(anyIterable);

Here we used the Array.from method to convert the iterable to an Array.

The other way I learned today was:

const anyIterable = document.querySelectorAll('a');
const convertedArray = [...anyIterable];

Here we made use of a combination of 2 things:

1. ES6 spread operator ...

When we prepend an iterable with ... (called the ES6 spread operator) what it does is it extracts all values from that iterable and replaces the ...anyIterable part of the expression with those values.

2. Array literal []

Then when we enclose the “spreaded” values with [ and ] it converts the whole thing into an array containing all the values from that iterable.

Both produce the same result. I don’t know if one performs better than the other under large data-sets. But even though the [...anyIterable] way is more concise, to me the Array.from(anyIterable) usage seems more readable.


That’s all folks, that was it for today. If you have anything unclear in this article or want to discuss anything else, hit me up on twitter @varun_barad.