Refresher Time: Javascript

crash course on the fundamentals

5 min readMar 12, 2021

Javascript is a programming language allows you to implement complex features on a webpage. Think of a car for instance. You have the make, parts and colors of the car (HTML & CSS) but what good is it if the car doesn’t have any cool functionality. Javascript is what makes the car rev loudly, accelerate to 100mph, drift, and everything else that makes it cool & dynamic.

Javascript is very complex and I probably won’t be able to cover every single topic out there in detail without writing a book but I will cover the basics I’ve learned so far because I sure do need a refresher. Also, keep in mind that Javascript != Java.

Variables: const, let, var

const: it is constant i.e. this variable cannot changed once it’s defined. it cannot be reassigned but it can be mutated.

let: you can reassign values.

var: var will always be global whereas let is not. var has been used since the beginning of Javascript but for the most part this isn’t used anymore ever since const and let was introduced in ES6.

Data Types: String, Numbers, Boolean

String

single quotes, double quotes or backticks/template literals'I live my life a quarter-mile at a time'
"now you owe me a 10 second car"
`I said a ${5*2} second car not a ${100/10} minute car`

Numbers

let speed = 50;
let degree = 65.5; // no floats in JS, can be a decimal
let horsepower = -20.5;

Boolean

let fast = false;
let slow = true;
console.log(10 > 2) //true
console.log(10 < 2) //false

Loops: for, while

for loop

while loop

Operators ( + , - , * , ** , / , %)

Switch Statements

great for cases with many conditionals

Functions

This is the bread & butter of JS. There are few ways to write a function.

Function Declaration

function yourFunction(){
   insert your code here
}yourFunction(); // this is how you call your function

Function Expression

A function is assigned to the variable explicitly. No matter how the the function expression is defined, it’s just a value stored in the variable addTotal. You can reassign addTotal to totalSum and it would still be the same outcome.

Arrow Functions

below is the same function but changed into an arrow function

Interaction: alert, prompt, confirm

Alert

Alerts simply show a message and waits for user’s confirmation.

Prompt

Prompts take in 2 arguments: title & default. The user can type something other than the default which will display once you click ‘ok’.

Confirm

Confirm shows a message and waits for the user to press “OK” or “Cancel”. It returns true for OK and false for Cancel.

Comparisons

Greater & less than: x > y, y < x.
Greater & less than or equals: x >= y, x <= y.
Equals: 5 == 5.SINGLE ‘=’ SIGN IS THE ASSIGNMENT OPERATOR.
Not equals:a != b. Bang operator is ‘opposite of’ so opposite of = is !=.

Code Structure: statements, semicolons, comments

statements: syntax & commands that perform actions

console.log('hello world')
alert('hello world')

semicolons: it may be omitted in most cases when a line break exists since JS does not strictly require it. Automatic Semicolon Insertion is a term when semicolons are added behind the scenes if it is needed.

comments: comments are used to temporarily ignore line(s) of code, make comments for reference, organization, etc.

// this comment won't run //
/* this too will be ignored by the engine */

Type Conversion: string, numeric, boolean

you may need to convert a number into a string, a boolean into a string or a value into true/false and this is where type conversion comes in handy.

String conversion: String() used when we need the string form of a value

let hot = true; 
console.log(typeof hot); // booleanhot = String(hot); // now hot is a string "true" 
console.log(typeof hot); // string

Numeric: Can be performed with Number(value). You cannot convert random text into a number for obvious reasons or else you’ll get NaN.

let randomNumber = "1234"; //string
randomNumber = Number(randomNumber);
console.log(typeof randomNumber) //number

Boolean: Boolean() will turn values into a TRUE or FALSE output.

console.log(Boolean(1)); // true 
console.log(Boolean(0)); // false  
console.log(Boolean("hello world")); // true 
console.log(Boolean("")); // false
console.log(Boolean(" ")); // true