Reversing a string using Object.keys() and .reduce?

#javascript #programming

We all use Object.keys() to get the keys of an object. Standard thing. So what happens when you get the keys of something else? The following is out of Lychen's REPL.

Lychen>let obj = {word:"bravo",translation:"shabaash"}
[undefined]
Lychen>Object.keys(obj).join()
word,translation

Yes, what we'd expect. What about an array?

Lychen>let arr = 'aap ka nam kya hai?'.split(" ")
[undefined]
Lychen>Object.keys(arr).join()
0,1,2,3,4

Hmm ... indices? Probably.

Lychen>const chabian = Object.keys(arr)
[undefined]
Lychen>arr[chabian[3]]
kya

Definitely.

Okay, what about a string?

Lychen>let str = "aap ki tabiyat kaisi hai?"
[undefined]
Lychen>Object.keys(str).join()
0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24

That bit of Urdu is 24 characters long. Let's see if it really is indices.

Lychen>const indices = Object.keys(str)
[undefined]
Lychen>str[indices[1]]
a
Lychen>str[indices[2]]
p

Looks like it.

And what about Object.keys of a number?

Lychen>const num = 58
[undefined]
Lychen>Object.keys(num).join()

Lychen>typeof Object.keys(num)
object
Lychen>Object.keys(num) === null
False

Hmm, so whatever the Object.keys of a number is, join returns an empty string, the typeof is object and it's not null.

Lychen>Object.keys(num) instanceof Array
True

Right. An empty array. Makes sense. I think.

So the routine. I'll leave it for others to test (I have and it's not particularly performant):

function Bruce_ObjectKeysReduce(string) {
  return Object.keys(string).reduce(function (acc, cur) {
    acc = string[cur] + acc;
    return acc;
  }, "");
}

(later)

That can be boiled down a little bit more, using ES6 forms, to

const Bruce_ObjectKeysReduce = (string) =>
    Object.keys(string).reduce((acc, cur) => {
      acc = string[cur] + acc;
      return acc;
    }, "");