const getFirstItem = (collection, cb) => {

// invoke the callback function and pass the first item from the collection in as an argument

cb(collection[0]);

};

const getLength = (collection, cb) => {

// Write a function called getLength that passes the length of the array into the callback

cb(collection.length);

};

const getLastItem = (collection, cb) => {

// Write a function called getLastItem which passes the last item of the array into the callback

cb(collection[collection.length - 1]);

};

const sumNums = (x, y, cb) => {

// Write a function called sumNums that adds two numbers and passes the result to the callback

cb(x + y);

};

const multiplyNums = (x, y, cb) => {

// Write a function called multiplyNums that multiplies two numbers and passes the result to the callback

cb(x * y);

};

const contains = (collection, item, cb) => {

// Write a function called contains that checks if an item is present inside of the given array.

// Pass true to the callback if it is, otherwise pass false

cb(collection.includes(item));

};

const removeDuplicates = (collection, cb) => {

// Write a function called removeDuplicates that removes all duplicate values from the given array.

// Pass the array to the callback function. Do not mutate the original array.

const newCollection = collection.slice();

for (let i = 0; i < collection.length; i++) {

if (collection.includes(collection[i], i + 1)) {

newCollection.pop(collection[i]);

}

}

cb(newCollection);

};

module.exports = {

getFirstItem,

getLength,

getLastItem,

sumNums,

multiplyNums,

contains,

removeDuplicates

};