arrays-of-objects.js

let animals = [
    {
        type: "cat",
        name: "Floof",
        votes: 0
    },
    {
        type: "dog",
        name: "Spot",
        votes: 0
    },
    {
        type: "cat",
        name: "Max",
        votes: 0
    },
    {
        type: "elephant",
        name: "Elle",
        votes: 0
    }
]

let emails = [
    {
        from: "fdsfds",
        unread: true
    },
    {
        from: "fdsfds",
        unread: false,
    },
];
const unread = emails.filter(e => e.unread);

// If the filter method ceased to exist, we could make our own
function myFilter(array, callback) {
    const filteredArray = [];

    // We could do this with a normal for loop instead
    // for(let i = 0; i < array.length; i++) {
    //     let item = array[i]
    //     const shouldKeep = callback(item) // either true or false
    //     if(shouldKeep) {
    //         filteredArray.push(item);
    //     }
    // }

    for(let item of array) {
        const shouldKeep = callback(item) // either true or false
        if(shouldKeep) {
            filteredArray.push(item);
        }
    }

    return filteredArray;
}

const unread = myFilter(emails, e => e.unread);

make-array-string.js

function makeArrayString(array, callback) {
    let string = "";
    for(let item of array) {
        string += callback(item) + "\n";
    }
    return string;
}