Getting Started with JavaScript

Getting Started with JavaScript

Introduction to Javascript

Console

The console is a panel that displays important messages - errors and stuff like that.

If you use console.log() then anything inside the parenthesis gets printed (logged) to the console. So this will print 42:

console.log(42);

Comments

You can do comments like this:

// This is a comment!

You can also do stuff like this:

console.log(print-important-thing); // This prints "print-important-thing"

Or you can do a multi-line comment thing:

/*
This is a really important thing I'm doing.
I'm so good at coding I have digestion problems.
I'm writing this on a plane.
And someone is watching over my shoulder
/*

You can even interrupt your own code with a comment!

console.log(/*IGNORE ME PLZ K THX BYE*/ 42); // This will still print 42 OMG LOL

Data Types

These can be:

• Numbers (1, 2, 3, 4, 5...and they do NOT need to be encapsulated in quotes. Even if you do like 10.25 it doesn't need quotes)

• Strings (a group of characters surrounded by single quotes or double quotes)

• Boolean (true or false)

• Null (the absence of a value)

• Undefined (noted with keyword undefined and is kind of like null but has different use)

• Symbol (unique identifiers. Won't worry about these for now)

• Objects (the first 6 things in this list are primitive (basic) data types, and objects are more complex)

Arithmetic Operators

You can do addition, multiplication, subtraction, division with the +, -, /, * signs. The remainder is %.

So you can do stuff like:

console.log(5+5);
console.log(65/5);
console.log(100-50);

String Concatenation

When '+' is used on two strings, it appends left string to right string. Like this:

console.log('Hello ' + 'World');

Properties

When you introduce a piece of data into JS program, the browser saves it as an instance of the data type. For example, the property of length contains the amount of characters in the string. You can use the dot operator plus the property you want to get its value.

For example, this will give a result of 2:

console.log('Yo'.length); // Prints 2

Methods

Methods are actions you can perform. You can "call" them by using the dot operator plus the name of the method. Like this:

'example string'.methodName()

Just don't forget that the method gets a '()' (I think) right after you use it. Check this example:

console.log('                        Remove whitespace                                           '.trim());

Built-in objects

An example is the 'math' object, and they rule cuz' they also have methods! So you can do something like this, which will create a random number between 0-1:

console.log(Math.random());

If you start generating random numbers, and multiplying them and other fun stuff like that, you might end up with weird decimals and stuff. So you can use a method called Math.floor() which rounds down to the nearest whole number.

Here's a tricky one:

console.log(Math.floor(Math.random() * 200));

This uses Math.floor to make the output of Math.random * 200 into a whole number.

Variables

Variables are like this:

var myName = 'Brian';
console.log(myName);
// This should print "Brian"

The way that myName is capitalized is known as camel casing.

Keep in mind that variables:

• Can't start with Numbers

• Are case sensitive

• Should probably not have two with similar capitalization - like myName and MyName

Once you set a variable, it's easy to print with:

console.log(myName);

Create a Variable: let

The let keyword means a variable can be reassigned a different value. Like this:

let favFood = 'Beets';
console.log(favFood); // should return nothing
favFood = 'pizza'
console.log(favFood); // should return pizza
favFood = 'tuna'
console.log(favFood); // should return tuna

You can also set a variable as nothing initially and then change it over time, like:

let favMovie;
console.log(favMovie); // should return nothing
favMovie = 'Childs Play from 1988'
console.log(favMovie) // should return 'Child's Play from 1988'
favMovie = 'Childs Play from 2019'
console.log(favMovie) // should return 'Child's Play from 2019'

Create a Variable: const

const is kind of like a var but can't be changed. Check this out:

const favMovie = 'Childs Play 3';
console.log(favMovie);
var favMovie2 = "Child's Play 2";
console.log(favMovie2);
const favMovie = "Child's Play 1";

If you run this you'll get an error saying the const has already been declared.

You need to give const a value. You can't just leave it empty like you can with let.

Mathematical Assignment Operators

With mathematical assignment operators, you can mess with the value of a variable like so:

let levelUp = 10;
levelUp += 5;
let powerLevel = 9001;
powerLevel -= 100;
let multiplyMe = 32;
multiplyMe *= 11;
let quarterMe = 1152;
quarterMe /= 4;

In the above example:

The value of levelUp: 15
The value of powerLevel: 8901
The value of multiplyMe: 352
The value of quarterMe: 288

The Increment and Decrement Operator

The variablename++ or variablename-- can increase or decrease the value of a stored value. For example:

let gainedDollar = 3;
gainedDollar++;
let lostDollar = 50;
lostDollar--;
console.log(gainedDollar);
console.log(lostDollar);

Console log says:

4
49

String Concatenation with Variables

We've been adding strings to variables, and the + operator can combine two string values even if they are being stored in variables. For example, I can the value of my favoriteAnimal and then use it in a sentence:

let favoriteAnimal = 'koala';
console.log('My favorite animal: ' + favoriteAnimal);

String Interpolation

Interpolate is another word for insert. With ES6 of JavaScript we can interpolate strings using template literals. Here's an example:

let myName = 'tenaciousB';
let myCity = 'Kickapoo';
console.log(`My name is ${myName}. My favorite city is ${myCity}.`);

In my opinion, it's way easier to use these template literals because the code is easier to read.

typeof operator

typeof operators help you figure out what type of thing a variable is. For example:

let newVariable = 'Playing around with typeof.';
console.log(typeof newVariable);
newVariable = 1;
console.log(typeof newVariable);

And the output will say:

string
number