what does .replace do in javascript code example

Example 1: javascript replace string

var str = "JavaScript replace method test";
var res = str.replace("test", "success");  
//res = Javscript replace method success

Example 2: js replace characters in a string

var str = "Original string!";
var str = str.replace("Original", "New");

Example 3: replace in string javascript

const p = 'hello world ! hello everyone ! ';

const regex = /hello/gi;

console.log(p.replace(regex, 'good morning'));
// expected output: "good morning world ! good morning everyone !"

console.log(p.replace('hello', 'good evening'));
// expected output: "good evening world ! hello everyone !"