What does this return?

const str = "HELLO";
console.log(str.toLowerCase());

Given:

const obj = {value:5};
const copy = obj;
copy.value = 10;

After running this:

div.style['background-color'] = 'yellow';

In reduce((acc,val) => acc + val, 0), why use 0?

Context:

Context:

const numbers = [1, 2, 3];
const mapped = numbers.map(num => num * 2);
console.log(mapped);

What will mapped contain?

What is the result?

const str = "frontend";
console.log(str.substring(0, 5));

Result of:

const str = "a b a";
console.log(str.replaceAll("a", "x"));