printHello.js

const characters = [
    {
        char: "h",
        position: [0]
    },
    {
        char: "e",
        position: [1]
    },
    {
        char: "l",
        position: [2,3,10]
    },
    {
        char: "o",
        position: [4,8]
    },
    {
        char: ",",
        position: [5]
    },
    {
        char: " ",
        position: [6]
    },
    {
        char: "w",
        position: [7]
    },
    {
        char: "r",
        position: [9]
    },
    {
        char: "d",
        position: [11]
    },
    {
        char: "!",
        position: [12]
    }
]
function printHello(characters) {
    const helloArray = [];
    characters.forEach(character => {
        character.position.forEach(position => {
            helloArray[position] = position === 0 ? character.char.toUpperCase() : character.char;
        })
    });
    console.log(helloArray.join(""));
}
printHello(characters);