How to replace a letter in an array?

Please help me how to change the letter in the array without creating a new array ?

Can you show us what code you have tried so far?

array[0].charAt(0) = “9”;

What does your full code look like?

What does arr look like?

If array[0] is a string, you can not mutate it. Strings are not mutable. You can create a new string and assign it to array[0] but you can not directly change a character of a string.

let array = [‘109’, ‘102’, ‘100’, ‘030’, ‘020’, ‘006’, ‘001’];

You have to fully replace array[0] since it is a string. You can’t just change part of it.

Side note - the more code you show, the easier it is for us to understand what’s going on.

For example, I need 101 to get 901.

Let’s say I have the following code:

let aString = `some string';

I can not do this:

aString.charAt(0) = 'S'

but I could do:

let newStr = 'S' + aString.slice(1);
aString = 'S' +  aString.slice(1);
console.log(aString); // displays "Some string"

Let’s just say that such a function should be replaced by 9 so that there is a maximum difference in the sum

let array = ['109', '102', '100', '030', '020', '006', '001'];
let k = 5;
let swith = 0;

function replacement(k, array) {
	for (let i = 0; i < k; i++) {
		for (let j = 0; j < array.length; j++) {
			let firstLetter = array[j].charAt(swith);
			if (firstLetter != "0" && firstLetter != "9") {
				let currentValue = array[j];
				if (minValue == null || currentValue < minValue) {
					minValue = currentValue;
			} else {


What should be replaced?

Maximum difference in what sum?

Maybe if you give us the full problem description, we can better help you. I am not understanding what the function is supposed to do and what swith or k is supposed to represent.