Intro to JavaScript Terms

As a primer to more in depth JavaScript discussions, I figured an intro to some of the terminology that we’ll be using might be helpful.  As this will not be a complete “Intro to JavaScript” (far from it, in fact), I’ll provide links to resources that I’ve found helpful along the way.


There are several sites that I use frequently in learning to code.  Obviously, freeCodeCamp is the main one.  As I mentioned in my first post, I am currently working through the front end development certification at freeCodeCamp and highly recommend it.  While working through the freeCodeCamp curriculum I use w3schools, MDN and Stack Overflow extensively as references.  I also found that Tutorial Republic is an excellent resource for HTML, CSS and Bootstrap (which is a powerful front end framework that makes creating responsive web pages much easier).

There are also a couple books that I’ve used along the way.  The first is ‘Eloquent JavaScript‘, which is an excellent free resource (available in print also) for learning JavaScript.  It’s not exactly a book for beginners, but the online version provides examples and problems that you can work through right in the browser.  It’s the best JavaScript resource I’ve found yet…   I also picked up the Head First books ‘HTLM and CSS‘ and ‘HTML5 Programming‘.  They’re more on the beginner side, but are written well and I found them helpful in learning to interact with the DOM (which we will get into in future posts).

Intro to Terminology

Now, to cover some terms we’ll be using frequently.  In future posts, I will have to assume a basic understanding of these languages, otherwise each post will be the length of a book.  So I urge you, if you have any questions about the concepts listed below, please use the resources listed above to read more about them.

In JavaScript, groups of data are called values and these values have types.  There are 7 data types in JavaScript:

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

Any of these data types can be stored in a variable.  To declare a variable, use the keyword ‘var’, as such:

The above statement created a variable named ‘a’.  It also includes a comment…  Anything written on a line after // is a comment and will be ignored by the browser.  You can also assign values to the variable when you create it. The following statements create variables and assign values of the various data types.

JavaScript provides several data structures called objects and arrays.  I plan on covering objects and arrays in depth in decipheredCode so for now will only cover each at a very high level.

Objects allow us to group data of various types (including other objects) as name:value pairs called properties.  Objects are used extensively in JavaScript, in fact JSON (JavaScript Object Notation) files are the way most programs pass data among themselves over the web.

An array is a list of objects or values, called elements, stored inside brackets and separated by commas.  Array elements can be accessed using bracket notation and indexes (note: first element in an array is index [0]).  An example of accessing the first element of an array would be:

The arr declared above would now have the string ‘apple’ as it’s first element (index [0]).  Chapter 4  of ‘Eloquent JavaScript’ gives a great explanation in the use of objects and arrays.

Another term used extensively in JavaScript, and programming in general, is function.  A function is a self contained block of code that can act on it’s own to do something.  A function can take a set of parameters (optional) and contains a block of code to act on those parameters.  Here’s an example of a function.

This function, named addOne, has one parameter (num).  The code inside the function creates a new variable called newNum, then sets newNum equal to num + 1 and returns the value of newNum.  The way we would use this function (or invoke it) is

This example calls the addOne function and passes the number 5 as an argument.  This function call would return the value 6.

What is an argument?  An argument is the actual value that you pass into the function, as opposed to a parameter, which is the name listed in the function definition.  I’ll be using these terms interchangeably here at decipheredCode (whether right or wrong…), so you can think of both arguments and parameters as something that gets passed into a function.

Now…  This has been a long, rambling post that mentioned a bunch of things but didn’t really explain anything in detail. I feel, however, that it was necessary before I started digging any deeper..  Hopefully, this will be helpful to someone just starting out on their journey to learn to code.  The next posts here at decipheredCode will start to dig into real problems.  Meantime, I urge anyone that is interested to check out the links that I mentioned above and to start getting their hands dirty by writing some code!


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