Basic Syntax of JavaScript

As in any programming language, JavaScript has a set of basic syntax rules that we must follow.

These rules define how to organize instructions and how to structure code so that the interpreter (the browser or the runtime environment) can process it without errors.

Let’s review them 👇

Instructions and Sequential Execution

In JavaScript, the code is composed of instructions that execute sequentially.

This means that the instructions run one after another, from top to bottom, in the order they appear.

let name = "Juan";
console.log(name);

Semicolon to End Statements

In JavaScript, each instruction generally ends with a semicolon ;.

let name = "Juan";
console.log(name);

However, the language allows you to omit it in many cases. To do this, it applies some rules called ASI (Automatic Semicolon Insertion).

Although JavaScript can generally infer the end of a line, it is good practice to always use a semicolon. Otherwise, it can lead to errors. We see this with a simple example.

const c = 1 + 2
(1 + 2).toString()

TypeError: 2 is not a function

const c = 1 + 2(1 + 2).toString()

const c = 1 + 2;
(1 + 2).toString();

'3'

Braces to Delimit Code Blocks

Braces {} in JavaScript are used to define code blocks, especially in control structures like functions, loops, or conditions.

All the code within the braces belongs to the same block and will execute together (for the interpreter, it’s as if it were a single instruction).

Example of a code block in an if structure:

if (name === "Juan") {
    console.log("Hello, Juan!");
}

Case Sensitivity

JavaScript is a language that is case-sensitive. This means it distinguishes between name, Name, and NAME, considering them different variables.

let name = "Juan";
let Name = "Pedro";

console.log(name); // Prints "Juan"
console.log(Name); // Prints "Pedro"

Variable Names and Naming Rules

When naming variables in JavaScript, there are certain rules we must adhere to:

1. Cannot start with a number. A variable cannot begin with a digit.

   let 1name = "Juan"; // Incorrect
   let name1 = "Juan"; // Correct

2. Cannot contain spaces. Variable names must be a single word without spaces.

   let my name = "Juan"; // Incorrect
   let myName = "Juan"; // Correct

3. Cannot include special symbols like !, @, #, %, among others, except for the underscore (_) and the dollar sign ($).

   let name$ = "Juan"; // Correct
   let _name = "Juan"; // Correct

4. Styling conventions. Although JavaScript does not require it, it is common to use camelCase for variable names, where the first word is in lowercase and additional words start with uppercase:

   let myExampleVariable = "Example";

Reserved Words

JavaScript has a list of reserved words that cannot be used as variable names, function names, or identifiers.

Some reserved words include:

These words are used by the language for specific functions, and using them as names will cause errors.