Homework Week 6

Topics discussed this week:
• Closures
• Scope
• Callbacks

Here you find the readings you have to complete before the seventh lecture.

Step 1: Feedback

Deadline Monday

Give feedback on step 2 of week 5 to one of your fellow students (do this by creating issues in Github).

Step 2: Git Homework

Deadline Saturday

Make these assignments. For handing in homework follow the Forking workflow that is described in our lecture-3.md file of HackYourFuture’s Git repository (there is also a video that explains this).

Step 3: Read

Read:

• JavaScript : Closures

• Everything you wanted to know about JavaScript scope

• JavaScript Scoping and Hoisting

• 5 JavaScript “Bad” Parts That Are Fixed In ES6

• More about closures

• A VERY popular StackOverflow article

Step 4: JavaScript

Deadline Wednesday

0. We learned a little bit about callbacks in JS. A callback is simply a function passed to another function that gets executed (run) after a potentially long running operation has completed. There is another function called setTimeout that will wait a specified period of time and then execute a function. For example:

function doIt() {
    console.log('I am done');
}
setTimeout(doIt, 5000)

f you run the above code it will wait 5 seconds and print I am done. Please read something about setTimeout on MDN. The first argument to the setTimeout call is the callback (doIt)

1.We saw that we can pass functions as arguments to other functions. Your task is to write a function that takes another function as an argument and runs it.

function foo(func) {
        // What to do here? 
}
    
function bar() {
    console.log('Hello, I am bar!');
}

foo(bar);

2. You must write a function that takes 4 arguments. - A start value - An end value - A callback to call if the number is divisible by 3 - A callback to use if the number is divisible by 5

The function should generate an array containing values from start value to end value (inclusive).

Then the function should iterate over the array and call the first callback if the array value is divisible by 3

The function should call the second callback if the array value is divisible by 5

Both functions should be called if the array value is divisible by both 3 and 5

THIS IS FAKE CODE 
function threeFive(startIndex, stopIndex, threeCallback, fiveCallback) {
    // make array 
    // start at beginning of array and check if you should call threeCallback or fiveCallback or go on to next  
}
threeFive(10, 15, sayThree, sayFive);

// Should create an array [10,11,12,13,14,15]
// and call sayFive, sayThree, sayThree, sayFive  - please make sure you see why these calls are made before you start coding

3. Please solve this problem using: https://www.freecodecamp.com/challenges/repeat-a-string-repeat-a-string
3.1 A for loop.
3.2 A while loop.
3.3 A do loop.

4. Some practice with objects https://www.freecodecamp.com/challenges/construct-javascript-objects-with-functions

5. Nested loops https://www.freecodecamp.com/challenges/nesting-for-loops

6. We did some work with arrays - var arr = [1,2,3] We can also nest arrays inside arrays like this var arr2d = [[1,2], [3,4], [5,6]] (for math people you can think of this as a matrix) How would you print all the items of an array with 3 dimensions? How about with K dimensions? What if you didn't know how deep the array was nested? (You don't have to write code for this but think about it)

7. Here are two functions that look like they do the something similar but they print different results. Please explain what's going on here.

let x = 9; 
function f1(val) { 
    val = val+1; 
    return val;
}
f1(x);
console.log(x);


let y = { x: 9 };
function f2(val) {
    val.x = val.x + 1;
    return val;
}
f2(y);
console.log(y);

If you are confused please run the code and then consult the Google for "javaScript pass by value pass by reference"

Step 5: Scope and Closures

Deadline Saturday

Let's continue to learn a little more about scope and Closures.

1. Write a function that would allow you to do this:

let addSix = createBase(6);
addSix(10); // returns 16
addSix(21); // returns 27

Bonus: Write a function takes this array ['a', 'b', 'c', 'd', 'a', 'e', 'f', 'c'] and returns an array which only has unique values in it (so it removes the duplicate ones). Make it a 'smart' algorithm that could do it for every array (only strings/number). Try to make it as fast as possible!

Step 6: Read before next lecture

Deadline Sunday morning

Go trough the reading material in the README.md to prepare for your next class

How to hand in your homework:
• Upload your homework in your "hyf-javascript2" Github repository. Make sure to create a new folder "week3" first. 
• Upload your homework files inside the week3 folder and write a description for this “commit”.
• Your hyf-javascript2/week3 should now contain an index.html, main.css and a script.js file (and the images folder)
• Place the link to your repository folder in Trello.