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Back to JS Basics

dandevri profile image Danny de Vries Updated on ・3 min read

JS is here to stay, without you I got trouble. To understand you here is a quick refresher on the basics of JavaScript.

We all read this article from a couple of years ago. (NO!? you've been living under a rock or something?) It's easy to get caught up in a JavaScript library and never get out. I've seen people know more about React and jQuery than pure vanilla JS.

When I started the Minor Web Development at the University of Applied Sciences Amsterdam I had (what Buddhist call) a beginner's mind.

It refers to having an attitude of openness, eagerness, and lack of preconceptions when studying a subject, even when studying at an advanced level, just as a beginner in that subject would.

People around me would sit behind their keyboard and start writing line after line of complex JS code. I would come in, and curious as I was, would ask 'simple' questions like;

Where does this function gets invoked?
What are the initial arguments of this function?
Where do you declare this variable?

And what bothered me is that some people couldn't give me straight up answers so I could learn from them. Don't get me wrong, most people are really great at handling complex JS stuff (and libraries) but to me it feels like they get caught up and lose sight of general JavaScript (programming) concepts.

So with this in mind I wanted to write a quick (yeah, you can call it a cheat sheet) refresher on basic JS concepts.

Programming vs Scripting.

People argue about if programming or programming language is really the correct term to describe JavaScript. JavaScript doesn't stand by itself, it needs to use a interpreter. In most cases this is the browser or a standalone JS engine. It isn't native machine code (binary 01010) but it needs to be compiled and that's where the browser comes into play.

To play it safe I would call JavaScript a scripting language which falls under the larger category programming language.


Variables store data and manipulate it. They do this by using a label to point to the data. In JavaScript data can be one of the following 7 data types:

  • undefined
  • null
  • boolean
  • string
  • symbol
  • number
  • object

They can store different values at different times.

  • To declare a variable: var keyword with myVarname of the variable.
  • Store value in a variable with the assignment operator: =
  • Initialize the variable with a data type: 19 (in this case a number)
var myVar = 19;

A variable that is only declared but has no initial value has the value of undefined.

var a; // value is undefined


You can divide up your code in reusable parts by using functions.

function myFunction() {
// do stuff

You can call or invoke the function by using the function name and place parentheses behind them.


parameters are basically variables that act as placeholders for the values that are to be input to a function when it's called. You pass a value as input to the function. Many people use the term parameter and argument interchangeably but there is a slight difference.

function myFunction(param1, param2) { // These are parameters
   console.log(param1 + param2);

myFunction(1, 2); // These are arguments

Values that are passed into a function when it is called are arguments. The placeholders are parameters.


With arrays you can store multiple data types in one variable. You declare it the same way as a variable but you put [] around the values and seperate each one with a comma. Every value in an array is called a entry.

You can access data inside array using indexes. Arrays use zero-based indexing. So the first item in the array starts with a 0.


Objects are similar to arrays, except that instead of using indexes you access the data in objects through what are called properties. Every property is made up of a key and a value.

var dog = {
  "name": "Peter",
  "legs": "4"

The stuff above is a basic outline of some of the core JavaScript terminology. Some of the stuff that I need to remind myself of on the daily. Stuff that people, IMHO, need to refresh more often. Hope this helps and next time you want to sound cool; try to use the right terminology. 👌

Thanks for reading! You can follow me on @dandevri and feel free to reach out to me if you have something to say!


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juanfrank77 profile image
Juan F Gonzalez

This. People get so caught up on the new shiny thing that they forget the very own fundamentals of the language itself. As one guy at work once told me "Whether you're and Angular or React or Vue or whatever else, that doesn't mean sht if you really don't know Actual JavaScript. Be proud of being a JavaScript developer, not a React developer"

dandevri profile image
Danny de Vries Author

A lot of frameworks (especially React) requires you to have strong fundamental knowledge of vanilla JavaScript. That doesn't mean React won't give you some core programming knowledge it's just that a lot of it will be 'magic' if you skip the basics.

Sloan, the sloth mascot
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dandevri profile image
Danny de Vries Author

Fixed it! Thanks for pointing that out.

qm3ster profile image
Mihail Malo

Awww, but I liked it!

dandevri profile image
Danny de Vries Author

That would indeed be a nice topic to write about! A bit more in-depth of how the browser parses and compiles JS.