How do I replace a character at a particular index in JavaScript?

Question

I have a string, let\'s say Hello world and I need to replace the char at index 3. How can I replace a char by specifying a index?

var str = \"h         


        

Answer 1

Generalizing Afanasii Kurakin's answer, we have:

function replaceAt(str, index, ch) {
    return str.replace(/./g, (c, i) => i == index ? ch : c);
}

let str = 'Hello World';
str = replaceAt(str, 1, 'u');
console.log(str); // Hullo World

Let's expand and explain both the regular expression and the replacer function:

function replaceAt(str, index, newChar) {
    function replacer(origChar, strIndex) {
        if (strIndex === index)
            return newChar;
        else
            return origChar;
    }
    return str.replace(/./g, replacer);
}

let str = 'Hello World';
str = replaceAt(str, 1, 'u');
console.log(str); // Hullo World

The regular expression . matches exactly one character. The g makes it match every character in a for loop. The replacer function is called given both the original character and the index of where that character is in the string. We make a simple if statement to determine if we're going to return either origChar or newChar.