On object manipulation in JavaScript

Honesty is important to me, even when it means coming clean about things I struggle with. Today, I confess that I struggle with comprehending object manipulation in JavaScript. Earlier this morning I was pairing with a friend on some katas in Code Wars, and I was struggling to understand what was happening with this code:

let staff = {
  tim: 'finance',
  jim: 'accounts',
  randy: 'canteen'
}

function boredom(staff) {
  var map = {
    accounts: 1,
    finance: 2,
    canteen: 10
 }

  var score = Object.keys(staff).reduce((a, b) => {
    return a + map[staff[b]]
  }, 0)

  return score <= 13 ? 'kill me now' : 'party time!!'
}

As you can see, boredom is taking in the staff object, where it wants to match up the staff values with the corresponding numbers in the map object, then tally the numbers to produce a score and return that score’s relevant string. So theoretically I understood all that, but not this specific part:

map[staff[b]]

My brain was reading it like this…

map.staff.b

…which is sort of right, but also why I was getting confused.
I mean, map and staff are two separate objects, not connected in any way, so how is that working? Let’s walk through it! And by let’s I mean me, so I can solidify my understanding 🙂

Alright, so the first time through, a is 0 and b is ‘tim.’ Which means map[staff[b]] is basically map['tim']. And what’s Tim’s value? It’s finance. Since Tim’s value is ‘finance,’ map['tim'] is basically map.finance. And what is map.finance? That’s right, it’s 2! So the first time through, 2 gets added to 0, and on the next time through 2 becomes a, and b is now ‘jim,’ and on and on until the numbers are reduced down and boredom spits out how you feel about your office’s fun level.

Check out the reduce method on MDN.

Find out more about objects in Eloquent JavaScript.

And don’t forget, you can walk through code step-by-step on this site.

Author: Ashly

I like learning, food, travel, and sports, and I love Salt Lake City.