JavaScript Playground

Learning Goals

Get more practice with JavaScript!


  • Variable A container for a value. The main building block for all programming
  • Function A predefined and reusable group of behavior
  • Expression An executable piece of code
  • Array A list of values
  • Operator Symbols that are used to assign, compare, and perform operations
  • Conditional An expression that evaluates to true or false, or a control flow statement that executes code

Lets go!

Open the console in your browser, and let’s get going!

Along the way, if your console gets too cluttered with text, then you can clear it by using the clear() command in the console.


// Let's create some vars!

// Create each of these variables in the console
// console.log each variable
// What do you expect to be logged for each var?

// What data type is each var?

var a = "A text string"

var b = 9

var c = 3*5

var d = "This" + " and" + " this"

var e = true

var 4isNotGood = 10

var @isNotGood = 10

var names = ["Marty", "Daphne", "Niles"]
// Variable assignment

var myVar = "To be"

myVar = "Or not to be"

// Before you run this command, what do you expect to happen?

// Why did that happen?

// Create a variable named ``newVar`` that is equal to the number ``1000``

// Create a variable `theta` and assign it with a string that is a sentence

// Create a new, separate variable for each of these data types: string, boolean, and number


// Make an array of three of your favorite animals

// Make an array of five numbers and three strings

// Make an array with ten names in it

// How do you get the first name from the array using indexing?

// How do you get the fifth name from the array?

// In your array of names, change the last name to a vegetable

// Now change the second name to your least favorite number

// Finally, add your favorite tree to the end of the array

// As a challenge, how do you get the last element of an array of any size?



// Assign a number to a variable
var numPizzas = 10

var numToppings = 2 * numPizzas

numPizzas = 25


// What did you expect here? Was the output different from what you expected?

somePizzaVar = 10

// What happened there?


// Add +, subtract -, multiply *, divide /, modulus %, increment ++, decrement --
// Work through each of these in your console
// Before you hit Enter, predict in your head what will be returned

12 + 53

"Turing" + " " + "School"

"String" + 10

13 + 4 * 6

(13 + 4) * 6

-1 + 3

5.3333 / 2

0 / 2

2 / 0

5.3333 % 2

2 % 2

var incrementMe = 50

var decrementMe = 50

Chain some more arithmetic operators together to see how the affect one another.

Logical and Comparison

// Identity operator ===
5 === 5

"All the words" === "All the words"

"All the words" === "All the words!"

2 === "2"

"true" === true

var aVar = 67
var bVar = 67
var cVar = "67"

aVar === bVar
aVar === cVar

// Negation operator !==
5 !== 5

2 !== "2"

true !== false

// And &&, Or ||, Not !
true && true

true && false

true  || true

false || true

false && true || true

false && (true || true)



There is also <, >, <=, >=. Create scenarios where you get true and false for each of these comparison operators.


// Structure of an if/else statement
if (condition_1) {
} else {

// Structure of an if/else-if statement
if (condition_1) {
} else if (condition_2) {
} else if (condition_n) {
} else {

It can get a little cumbersome to write if/else statements in the web browser’s console. There is a website called JS Bin that lets you write multiple lines of JavaScript and test it in the console.

Click here to use JS Bin with JavaScript and the console.

// What will happen with this conditional?
var isFalse = false;

if (isFalse) {
  console.log("Did it get here?")

Write an if/else statement where the first condition is satisfied.

Write another if/else statement where the else condition is satisfied.

// Conditional with logical operators

// Before you type this, what do you think will happen?
var isFalse = false;
var isTruth = true;

if (isFalse && isTruth) {
  console.log("First condition!");
} else if (isFalse || isTruth) {
  console.log("Second condition!");
} else {
  console.log("Last condition!");

When you’re done looking at if/else statements, research the switch statement to see how it behaves.


function sayHello() {


// What will be logged?

function divides(a, b) {
  return a / b;

console.log(divides(10, 5));

// What will be logged?

// Now it's your turn

// Write a function that does not take any arguments, and it logs "Wow, it worked!" to the console

// Write a function that does not take any arguments, and it returns your favorite movie as a string
// console.log the result

// Write a function that takes one argument, a number, and multiplies that number by 100
// console.log the result

// Write a function that takes one argument, your name, and puts your name in the middle of a sentence
// console.log the result

// Write a function that takes three numbers as arguments and returns the largest number
// The numbers should be able to be specified in any order

// What do you think will happen here? Anything bad?

function conCat(first, second, third) {
  return first + second + third;

var result = conCat("What ","gives? ");


// Are you surprised?

Additional Practice and Resources

When you search for JavaScript questions, you will often find a link to W3Schools. This site is…meh. It’s really not the most organized or thorough resource. A clearer and more thoughtful source of documentation is called MDN (Mozilla Developer Network). Here is MDN’s JavaScript documentation.

Practice, practice, practice! Repetition, repetition, repetition!

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