shoppingList.js

function shoppingList(input) {
    let index = 0;
    let list = input[index].split(`!`);
    index++;
    let commandList = input[index];
    index++;

    while (commandList !== "Go Shopping!") {
        let commands = commandList.split(` `);
        let command = commands[0];
        let item = commands[1];

        if (!list.includes(item) && command === "Urgent") {
            list.unshift(item);
        }

        if (list.includes(item)) {
            let itemIndex = list.indexOf(item);
            switch (command) {
                case "Unnecessary":
                    list.splice(itemIndex, 1);
                    break;
                case "Correct":
                    let itemNew = commands[2];
                    list[itemIndex] = itemNew;
                    break;
                case "Rearrange":
                    list.splice(itemIndex, 1);
                    list.push(item);
                    break;
            }
        }
        commandList = input[index];
        index++;
    }
    console.log(list.join(`, `));
}

shoppingList(["Tomatoes!Potatoes!Bread",
    "Unnecessary Milk",
    "Urgent Tomatoes",
    "Go Shopping!"]);
shoppingList(["Milk!Pepper!Salt!Water!Banana",
    "Urgent Salt",
    "Unnecessary Grapes",
    "Correct Pepper Onion",
    "Rearrange Grapes",
    "Correct Tomatoes Potatoes",
    "Go Shopping!"]);