String Replace in JavaScript

In JavaScript, you can replace part of a string using the replace() method:

s.replace(old, new)      // replaces first occurrence
s.replaceAll(old, new)   // replaces all occurrences

Here are some examples:

let sentence = "I love cats";
let result = sentence.replace("cats", "dogs");
console.log(result);  // "I love dogs"

let text = "aaa";
console.log(text.replace("a", "b"));     // "baa"  (only first!)
console.log(text.replaceAll("a", "b"));  // "bbb"

replace() returns a new string — the original is not modified.