Notes on Day 4 of 30 Days of JavaScript

• notes • series • javascript • javascript30

I believe I am well-versed with the latest JS array methods but I managed to learn new techniques today!

Table of Contents

Lessons Learned

const people = [
  'Bernhard, Sandra', 'Bethea, Erin', 'Becker, Carl', 'Bentsen, Lloyd',
  ...
  'Birrell, Augustine', 'Blair, Tony', 'Beecher, Henry', 'Biondo, Frank'
];

String.prototype.localeCompare()

The 7th challenge in the activity was to sort the items in the people array by last name:

My first thought was to use a custom function for Array.prototype.sort() to compare the last names similar to integers and I found the localeCompare method.

I kept getting the following error message that frustrated me:

"TypeError: a.localCompare is not a function

and I even tried to check the type of the names and they are all Strings! I realized it was “locale” with an e and not “local”.

Fortunately it worked as

peopple.sort((a, b) => a.localeCompare(b.toString()))
//

Lastly I tried using sort() as it is without any callback and it worked for some reason. But I do not recommend this because it might just be my browser. I will just stick to the callback way at least we are sure of the operations applied.

Array.prototype.reduce() accumulator for unique items

The last challenge was to return the occurrences of elements in an array (the result’s data structure wasn’t stated).

const data = ['car', 'car', 'truck', 'truck', 'bike', 'walk', 'car', 
  'van', 'bike', 'walk', 'car', 'van', 'car', 'truck' ];

My initial plan was to map over the items and create a Set for uniqueness of elements then save the number occurrences based on it. The solution was far more elegant than my approach because it just used the reduce method:

data.reduce((obj, item) => {
  if(!obj[item]) obj[item] = 0
  obj[item]++
  return obj
}, {})

I never thought that the second parameter (the initial value) would be useful in this approach. If we try to run the same code without the empty object, it will just return "car" ad the first element.

References

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