WELCOME, my dear coders, to the first chapter of the Getting started with the javascript series. I hope you are all having a great codelicious day! In the series, I will concentrate especially on the beginners. We will start from the very beginning and the very basics of the JavaScript programming language. So let's conquer the dragon and complete this quest that will improve and build your knowledge.

JavaScript is an important language because it is the language of the web browser. Its association with the browser makes it one of the most popular programming languages in the world. JavaScript is a scripting language and as with most scripting languages it is being interpreted, rather than compiled, so it is considered as a fast programming language (of course depending on the skills it may also be a slow programming language). The beauty of the javascript programming language si that when you make changes to your code - javascript script - you can test those changes immediately; You don't have to compile the script file first. Skipping the compile step saves a great deal of time during the debugging stage of Web page development. Last but not least, modern technologies provide you to use of javascript on the Front-End as well as on the Back-End, which is kinda neat, but the pros and cons of that approach are a part of a totally different topic.

In the above section, I mentioned the "compiling" and "interpreting". And I feel obligated to explain as simple as I can, what the compiler is and what is compiling vs what an interpreter is, and what is interpreting.

Generally speaking, a function is a "subprogram" that can be called by code external (or internal in the case of the recursion) to the function. In JavaScript, functions are first-class objects, because they can have properties and methods just like any other object. What distinguishes them from other objects is that functions can be called. In brief, they are Function objects. Every function in JavaScript is a Function object. See Function for information on properties and methods of Function objects.

To return a value other than the default, a function must have a return statement that specifies the value to return. A function without a return statement will return a default value. In the case of a constructor called with the new keyword, the default value is the value of this parameter. For all other functions, the default return value is undefined.

The parameters of a function call are the function's arguments. Arguments are passed to functions by value. If the function changes the value of an argument, this change is not reflected globally or in the calling function. However, object references are values, too, and they are special: if the function changes the referred object's properties, that change is visible outside the function.

Function declaration:

function name([param[, param[, ... param]]]) {
   statements
}

name - The function name.
param - The name of an argument to be passed to the function.
statements - The statements comprising the body of the function.

A function expression is similar to and has the same syntax as a function declaration. A function expression may be a part of a larger expression. One can define "named" function expressions (where the name of the expression might be used in the call stack for example) or "anonymous" function expressions.

Function expression:

function [name]([param[, param[, ... param]]]) {
   statements
}

name - The function name. Can be omitted, in which case the function becomes known as an anonymous function.
param - The name of an argument to be passed to the function.
statements - The statements comprising the body of the function.

An arrow function expression has a shorter syntax and lexically binds this value

([param[, param]]) => {
   statements
}

param => expression

param - The name of an argument. Zero arguments need to be indicated with (). For only one argument, the parentheses are not required.
statements - Multiple statements need to be enclosed in brackets. A single expression requires no brackets. The expression is also the implicit return value of the function.

Immediately Invoked Function Expression is a JavaScript function that runs as soon as it is defined.

(function () {
    statements
})();

Example of an IIFEE FUNCTION:

var result = (function () {
    return Math.PI;
})();
// Immediately creates the output:
console.log(result); // "3.141592653589793"

References:
School notes...
School books...

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