const getFirstItem = (collection, cb) => {

cb(collection[0]);

};

const getLength = (collection, cb) => {

cb(collection.length);

};

const getLastItem = (collection, cb) => {

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

};

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

const numSummed = x + y;

cb(numSummed);

};

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

const numProduct = x * y;

cb(numProduct);

};

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

cb(collection.includes(item));

};

const removeDuplicates = (collection, cb) => {

const itemsChecked = [];

collection.forEach((item, index) => {

if (itemsChecked.indexOf(item) === -1) {

itemsChecked.push(item);

}

});

cb(itemsChecked);

};

module.exports = {

getFirstItem,

getLength,

getLastItem,

sumNums,

multiplyNums,

contains,

removeDuplicates

};