I was doing some code challenges at Leetcode using Javascript language, and surprisingly converting the string into array improved the runtime then accessing the character directly via index.

Let me explain in code therms:

First

Accessing string directly via index srt[i] or str.charAt() takes at least 60ms.

let str = 'leetcode';
for (let i = 0; i < str; j++) {                  	
		let w = str[i]; // same as str.charAt(i)
		// do some with w
}

Second

Converting a string to array improved the runtime to approximately 40ms. Why? Shouldn’t this method be more time consuming since I’m converting data types?

let arr = 'leetcode'.split(''); 
for (let i = 0; i < arr; i++) {                  
		let w = arr[i];   //
		// do some with w
}

The same happens when using the spread operator.

let word = [...'leetcode’];
// ['l', 'e', 'e','t', 'c', 'o','d', 'e'] //

I’m still looking for an answer to this question. Let me know if you have a clue. ;)