Find length of string in Javascript (no built-in methods) recursively

Question

Here's a tough question which I'm unable to solve.

Write a recursive function that accepts a string and returns its length. Do not use the .length property, loops, or any built-in methods in Javascript to find the solution.

I'm quite close with this solution but I'm not able to find an alternative to the .slice() method. This function currently works but doesn't fit the question's parameters because if uses that method, and the .length property:

let lengthGetter = (str, def) => {
  let len = def || 0;
  if (str[0] === undefined) return len;
  return lengthGetter(str.slice(0, str.length - 1), len + 1);
};

console.log(lengthGetter("hello")) // 5

Even if it involves throwing away my current function, can anyone find a solution to this problem? Keep in mind you can't use any built-in methods or loops, which makes it quite challenging.

You can check for the presence of a character with simplly str[n]; if that's undefined it means you're beyond the end of the string (or before the start). — Pointy
– Pointy, Commented Mar 26, 2021 at 16:10

Rajender Joshi · Accepted Answer · 2021-03-26 16:17:22Z

4

This is the easiest recursive one-liner you can make to get the length of the given string without using any built-in methods.

const getLength = (str = "", length = 0) => str[length] ? getLength(str, length + 1) : length;

Sample:

const getLength = (str = "", length = 0) => str[length] ? getLength(str, length + 1) : length;

console.log(getLength("hello"))
console.log(getLength("helloworld"))

answered Mar 26, 2021 at 16:17

Rajender Joshi

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2 Comments

Scott Sauyet Over a year ago

Well, using the fact that strings are iterable, this might be even easier: const len = ([s, ...ss]) => s == undefined ? 0 : 1 + len (ss)

Rajender Joshi Over a year ago

That's more neat.

Ely · Accepted Answer · 2021-03-26 16:23:23Z

2

Close to what you have written:

let lengthGetter = (str, pos = 0) => {
  if (str[pos] === undefined) return 0;
  return 1 + lengthGetter(str, pos + 1);
};

answered Mar 26, 2021 at 16:23

Ely

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Comments

customcommander · Accepted Answer · 2021-03-26 18:47:26Z

2

This often comes as a surprise:

'🌯🌯🌯'.length
//=> 6

If you need to count what humans would see then you can destructure the string as most (but not all) characters would be preserved as such:

[...'🌯🌯🌯'].length
//=> 3

So we can have:

const Nil = Symbol();
const len = ([x = Nil, ...xs]) => x === Nil ? 0 : 1 + len(xs);

len('foo');
//=> 3
len('🌯🌯🌯');
//=> 3

edited Mar 26, 2021 at 18:47

answered Mar 26, 2021 at 18:42

customcommander

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