how to flip letters in a string javascript code example

Example 1: javascript string reverse

"this is a test string".split("").reverse().join("");
//"gnirts tset a si siht"

// Or
const reverse = str => [...str].reverse().join('');

// Or
const reverse = str => str.split('').reduce((rev, char)=> `${char}${rev}`, '');

// Or
const reverse = str => (str === '') ? '' : `${reverse(str.substr(1))}${str.charAt(0)}`;

// Example
reverse('hello world');     // 'dlrow olleh'

Example 2: reverse string js

function reverseString(str) {

    var newString = "";

    for (var i = str.length - 1; i >= 0; i--) { 
        newString += str[i]; 

    return newString;
}
 
reverseString('hello');