Training - Javascript Functions

Fork this repository to your GitHub account, then clone your GitHub copy onto your computer. Write the functions assigned below in the file functions.js.

Setup

Handwrite a first draft of each of these functions on your table, a whiteboard, or a notebook. We're doing this to get you feeling comfortable with interview-type procedure. This might seem intimidating, but there are some basic steps that you can always take.

1. Create a stub. This is a dummy version of your function with the function name, any parameters, and a hardcoded return value of the correct data type. While this is simplistic, it allows you to check in on the essentials of the function to make sure you understand how many parameters you need, what data type you should return, and what you should name this function. Interviewers will be pumped when you:

   • confirm the necessary parameters
   • return a value of the proper data type
   • name your function semantically

2. Define any necessary variables. If your function isn't returning a hardcoded value (most don't), you're probably going to return a variable. Define that variable with a concise, descriptive name and adjust the return statement as needed. Are there any obvious variables that you will need to complete the function? Define those with good names too!

3. Pseudocode the machinery of the function. Give yourself some idea of how you'll expand the function to do what you need it to do. When you handwrite code, it's hard to land on exact syntax. Instead of focusing on syntax, form a general sense of how you'll build the function. Will you need to loop? Will you need a certain conditional statement? Write this out in a format somewhere between english and code.

4. Refine your ideas into more formal code. Once you have a draft in pseudocode, you're ready to try to write more exact syntax. For now, don't get stuck on any single piece of syntax, but do your best to get as close as you can. This is a good test to see how much syntax you know by heart.

Once you've spent 5-10 minutes without a computer, enter your code into functions.js. Run your function by making a function call in the functions.js file, going to your terminal (which must be focused on the correct directory), and running node functions.js.

Unless a different behavior is specified, have the function log the proper response to the console AND return it.

Notice there is a solutions.js file. Make a full attempt at finishing these on your own and refer to the solutions when you are finished or stuck. Do not give up before you've made a good attempt! The discomfort of the struggle is the feeling learning! Also recognize that the solutions are only one solution and that there are many good ways to solve these problems.

For some of the problems, you'll have to use functions or other variables supplied by JavaScript's built-in Math object. Here is the documentation on using the Math object.

Example Usage of Math

	var absoluteValue = Math.abs(-4);
	//  absoluteValue will now be 4

	var fourSquared = Math.pow(4, 2);
	//  fourSquared will now be 16

	var roundedToNearestInteger = Math.round(1.22343);
	//  roundedToNearestInteger will now be 1

Function Definitions!

1. Build your own concatenation

Return a new string that is the combination of two string arguments passed into the function

Example: 'dog' and 'house' will return 'doghouse'

Function signature (only look at this after you've thought about what it should look like)

function combineWords(word1, word2) {
	// TODO: Place your code here
}
var result = combineWords('dog', 'house');
console.log(result);
// displays 'doghouse'

2. Repeat a phrase

Display an argument phrase to the console n times

Function signature (only look at this after you've thought about what it should look like)

function repeatPhrase(phrase, n) {
	// TODO: Place your code here
}

repeatPhrase("Hello", 5);
// displays
// Hello
// Hello
// Hello
// Hello
// Hello

3. Build your own Power function

Return number ^power without using built-in Math functions

Example:
4⁵ = 4 * 4 * 4 * 4 * 4 = 1024

Function signature (only look at this after you've thought about what it should look like)

function toTheNthPower(number, power) {
	// TODO: Place your code here		
}

var result = toTheNthPower(4, 5);
console.log(result);
// displays 1024

4. Area of a circle: π r²

Return the area of a circle given the radius
background information

Function signature (only look at this after you've thought about what it should look like)

function areaOfACircle(radius) {
	// TODO: Place your code here
}

var result = areaOfACircle(2);
console.log(result);
// displays approximately 12.57

5. Pythagorean Theorem: a² + b² = c²

Return c given a and b
background information

Function signature (only look at this after you've thought about what it should look like)

function pythagoreanTheorem(a, b) {
	// TODO: Place your code here
}

var result = pythagoreanTheorem(3, 4);
console.log(result);
// should display 5;

6. Is X Evenly Divisible by Y ?

Return a boolean value whether or not X can be divided by Y without any remainders.

Hint: Explore the world of Modulus operators!

Function signature (only look at this after you've thought about what it should look like)

function isXEvenlyDivisibleByY(x, y) {
	// TODO: Place your code here
}

var result = isXEvenlyDivisibleByY(99, 3);
console.log(result);
// displays true

7. Vowel Count:

Return the number of occurrences of vowels in a word. Vowels are a, e, i, o, u, and y

Function signature (only look at this after you've thought about what it should look like)

function countVowels(word) {
	// TODO: Place your code here
}

var result = countVowels("stealing");
console.log(result);
// displays 3

*Challenge: Can you alter the code to count both upper case AND lower case?*

8. Does the array contain "wdi"?

Given an array, return true if it contains the string "wdi" and false if it does not contain that string.

findWdi([9,'Bart Simpson', true, 'wdi']) // returns true
findWdi(['a','b','c']) // returns false

Function signature (only look at this after you've thought about what it should look like)

	function findWdi(arr){
		// TODO: Place your code here
	}

9. Find the longest word in a sentence

Given a string representing a sentence, return the longest word in that sentence.

Function signature (only look at this after you've thought about what it should look like)

findLongestWord("The rain in Spain falls mainly on the plain"); // => "mainly"
findLongestWord("abcdefghijkl"); // => "abcdefghijkl"

function findLongestWord(sentence) {
    // TODO: Place your code here
}

10. Build an ASCII Triangle!

Display a simple triangle with asterisks

Example:
printTriangle(5)

*
**
***
****
*****

Function signature (only look at this after you've thought about what it should look like)

function printTriangle(length) {
	// TODO: Place your code here
}

printTriangle(3);
// displays
// *
// **
// ***

11. Create a heads-or-tails game.

In a separate file, create a super-simple HTML page that contains an element with the id result, and link your HTML page to a js file. In that js file, define 3 functions: -A function that returns either "heads" or "tails", the result of a coin flip. -A function that, when called, prompts the user to guess either "heads" or "tails" and returns their guess. -A function that takes in a string and puts that string into the result element on your page.

Then, write a fourth function that wraps all of these functions into one, so that calling that fourth function will prompt the user to guess heads or tails, flip a coin, and then tell the user whether or not they were right. Make sure that calling just that function from the console works as expected.

12. Stretch Challenge: Can you alter the printTriangle function to create a Pyramid?

Example: printPyramid(10);

           *
          * *
         * * *
        * * * *
       * * * * *
      * * * * * *
     * * * * * * *
    * * * * * * * *
   * * * * * * * * *
  * * * * * * * * * *

Warning: This is a surprisingly tricky interview-level exercise. Try at your own risk!

function printPyramid(length) {
	// TODO: Place your code here
}