Program Structures

Learning programming is very less about memorizing the cryptic syntactic sugars and more of the programming fundamentals itself the bits which makes a program. Because the fundamentals are the same everywhere, across all programming languages - the syntactic sugars differ.

Although we will be using JavaScript to understand the concepts and the glossy details. But rest assured most of the concepts are shared across all programming languages.

Let us quickly go through the scope of this blog.

Table of contents

Expressions

• Every block/line of code that produces a value is called an expression.
• Every value written literally like 'Programmer' or 'JavaScript' or any numerics like 2 is an expression.
• An Expression within a parenthesis (expression) is also an expression.
• Unary or Binary Operations involving expressions is also an expression.

This is the beauty of language based interface - as most of English can be directly used in logic formation and deductions.

Consider the following example below :

If the program has bugs or the program involves division by 0. The program will crash.

This is an excellent example of the beauty of language based interface. The above example is really comprised of two sentences :

• If the program has bugs

OR

• If the program involves division by 0

We used two sub sentences to form a single sentence - and similarly two sub expressions to form a single expression.

The above example is essentially a conditional statement, in the form of if(p or q) then r.
Where p , q, r are just statement variables which can be substituted by actual english.

If an expression corresponds to a sentence fragment, a JavaScript statement corresponds to a full sentence. A program is a list of statements.

Note : A statement is an expression that has a consistent truth value. i.e, it can either be true or false but never both. On the contrary, a sentence is an expression that bears inconsistent truth values meaning for some cases it may be true and other cases false.

Statements

We introduced the fundamenetals of statements just a few lines ago.
The simplest statement in programming paradigm is an expression that ends with a semi-colon.

Example :

Hello World;
!false;

That is it. That is a statement. Although very trivial and useless admittedly, but does not change the fact that the above lines are two statements.

🎯 A statement only amounts to something when it affects the environment(in context of the program scope). It could be something as simple as printing something on the console or updating a variable which is then used by some other block of code. Either cases the statements are likely to affect the program and it's state. These changes and similar changes alike are called SIDE EFFECTS .

Note: JavaScript is lenient sometimes and ignores missing semi-colons in certain cases. But the best practice would be to use them - in order to ignore the nuances of missing terminating characters.

How does JavaScript keep an internal state or remember values? 🤔

To catch and hold values, JavaScript uses something called Bindings or simply variables.
Consider the snippet below :

let Greet = "Hello World, JavaScript is amazing!";

The above line is literally indicating a binding and it is another kind of statement.

• The special keyword let indicates that the sentence is going to define a binding.
  (More about these special keywords, soon)

• Followed by the name of the binding.

• And we immediately assigned a value to the binding by using the = and an expression, which is Hello World, JavaScript is amazing!

Note: = in programming is assignment operator. Not equality operator!

By the example statement - it creates a binding called Greet to point towards the value Hello World, JavaScript is amazing!

When a binding points towards a value - it does not essentially gets tied to it forever.
Meaning, that at any point of time, we can use the = operator again on existing bindings to make it point towards a new value.

Continuation of the previous example :

let Greet = "Hello Reader";

let Question = "How are you liking JavaScript?";

As obvious as it seems - we made the binding named Greet point to a new value now. And also defined a new binding named Question.

When bindings are defined, we can use their names as expressions. Example :

let Greet = "Hello Reader";

let Question = "How are you liking JavaScript?";

let Welcome = Greet + Question;

// the binding named welcome will hold the value "Hello Reader How are you liking JavaScript?"

The above example may seem a little cryptic if you are an absolute beginner to programming. But what it is doing essentially is just concatenating two strings because we used an expression that includes a binary operation between two expressions Greet + Question

Consider a simple example for usage of defined bindings as expressions.
Imagine Santa Clause 🎅 gives you 1000$ on Christmas and again 2000$ on New Year's eve.
The equivalent code will look like :

let FirstGiftBySanta = 1000;

let SecondGiftBySanta = FirstGiftBySanta + 2000;

console.log(SecondGiftBySanta);
//output : 3000 (1000 + 2000)

When you define a binding, and do not assign it any value to point at, it ends up pointing to a bogus address/garbage values. Hence if you try to retrieve the value of such a binding you are likely to see undefined

But, you can assign a value to it later in your code. Example :

let LuckyNumber;

console.log(LuckyNumber);
//output : undefined

LuckyNumber = 3;

console.log(LuckyNumber);
//output : 3

Note: To assign value to a pre-defined binding you do not have to implictly use the special let keyword again. Why? We have already used it to define a binding LuckyNumber in the above snippet.But not essentially asked it to point at a value. So in order to make a predefined binding point at something, we just simply use the = operator and the expression we want the binding to grab or point at.

You can also use a single special let keyword to define more than bindings seperated by a comma. Like :

let WholeNumber = 0,
  NaturalNumber = 1,
  EvenNumber = 2;

console.log(Wholenumber + NaturalNumber + EvenNumber);
//output : 0 + 1 + 2 = 3

At this moment, let us not get into the nuances of the special keywords like let, var, const
Although similar, they have subtle difference.
Check them out in details here, in this fine blog by FreeCodeCamp : let vs. var vs. const in js

Binding Names

Naming identifiers or bindings or variables is one of the things most people struggle with. But the best practise is naming it in such a way that is self explanatory and relevant to it's purpose.

Consider the below snippet :

let x = "Sweet";

console.log(x);
//output : Sweet

let Dessert = "Sweet";

console.log(Dessert);
//output : Sweet

Both the code blocks essentially does the same thing and produces the same value. But they differ largely in the way they are defined. A person can't just read x, and guess what it is pointing at, on the other hand the variable Dessert is much more sensible than just x. So any person reading the code can guess what the variable Dessert is all about and be completely clueless about x, unless they get to line where x is defined.

Although it does not make much sense or difference in toy programs like these, but in real world scenarios where the codebase is usually large and messy - naming convention has to be followed for better productivity and not waste time guessing what an identifier identifies!

Naming conventions

• Use identifiers relevant to it's purpose and avoid random variables.
• You can use characters, numerics to name variables but don't start a variable name with a digit.
• You can use sepcial characters like _ or $ to name variables, but no other special characters.
• You can not use reserved keywords to name variables.

Reserved keywords are the bindings used by the program itself, native bindings of the program. Some examples of reserved keywords in JavaScript are :
catch try finally console propmt window process... etc.
The list is super long and does not need to be memorized.

Environment

The ecosystem within which all the bindings and their values exist at a given point of time is called the environmet or in a more fancy term the world of the program.
On startup, the environment is not empty as it contains the native bindings that are part of the program itself.Bindings like the reserved keywords and etc.

Conventions Of writing well-designed programs

There is no single answer to good coding conventions, just a few shared practices amongst developers keeping readability, reusability and maintainability in mind. Below are some aspects that when taken care of can skyrocket productivity.

• Identifiers - Let us agree that naming bindings/varaiales or more mathematically identifiers is hard. It is really tempting to give it a random name to save time (which is totally okay for testing and trials) but it comes with more problems than benefits. Random names are not explanatory and anyone reasing the code will certainly be lost trying to guess what the identifier identifies, unless they get to the line where the identifier is defined. The best convention is to assign self explanatory, and names relevant to the binding's purpose. Hence, ditch all those x , y , z as far as possible and go for userInput, arrayOfShoppingItems, primeNumber.

• Indentations - This is one of the aspects that makes codes more readable. Honestly, the computer does not care if you are indenting the codes or writing everything in a single line. Infact, you can write an entire program in a single line and if it is correct it will execute just fine. More interestingly, the machine codes that all the codes we write ultimately gets converted to (by the compiler software) for the computer to read and execute is a giant cryptic line of code which is super messy and absolutely not comprehensible by human. But the purpose of indentation is to make the code more readable - so that in the future you, the programmer or any other programmer working on the codebase can actually visually discern between the each statements and hence read the codes efficiently.

• Terminating Character - Though there are some cases where absence of a ; does not affect the program(in High-level languages only). But it is the best practice to use it so as to save the nuances of remembering the scenarios where a ; matters and where not.

That is it. Congratulations for writing your very own program 🎊

Acknowledgements and Hyperlinks

• Cover Image: Google
• FreeCodeCamp: let vs. var vs. const