4. Basic Syntax

Statements and Expressions

Statements

Statements perform actions and don't return values:

let x = 5;        // Variable declaration
console.log(x);   // Function call
if (x > 3) {       // Conditional
    x = x + 1;
}

Expressions

Expressions return values:

5 + 3              // Arithmetic expression
x > 3              // Comparison expression
"Hello " + "World" // String concatenation

Semicolons

Semicolons are optional in JavaScript, but recommended:

// Good practice
let a = 1;
let b = 2;

// Also valid (automatic semicolon insertion)
let c = 3
let d = 4

Comments

// Single-line comment

/*
Multi-line
comment
*/

/**
 * JSDoc comment
 * @param {string} name - The name parameter
 */
function greet(name) {
    return `Hello, ${name}!`;
}

Case Sensitivity

JavaScript is case-sensitive:

let myVariable = "Hello";
let myvariable = "World"; // Different variable

Whitespace

Whitespace is generally ignored:

// All these are equivalent
let x=1+2;
let x = 1 + 2;
let x   =   1   +   2;

// But be consistent for readability

Code Blocks

Code blocks are enclosed in curly braces:

if (condition) {
    // Code here runs if condition is true
    statement1;
    statement2;
}

Identifiers

Rules for naming variables, functions, etc.:

• Must start with letter, underscore (_), or dollar sign ($)
• Can contain letters, numbers, underscores, dollar signs
• Cannot be reserved words
• Case-sensitive

Valid identifiers:

myVariable
_myVariable
$myVariable
myVariable123

Invalid:

123variable    // Cannot start with number
my-variable    // Hyphens not allowed
var            // Reserved word

Reserved Words

Some words are reserved and cannot be used as identifiers:

// Complete list of reserved words:
break, case, catch, class, const, continue, debugger, default, delete,
do, else, enum, export, extends, false, finally, for, function, if,
implements, import, in, instanceof, interface, let, new, null, package,
private, protected, public, return, static, super, switch, this,
throw, true, try, typeof, var, void, while, with, yield

Literals

Literals are fixed values:

// Number literals
42
3.14
0xFF    // Hexadecimal
0b1010  // Binary
0o777   // Octal

// String literals
"Hello World"
'Hello World'
`Hello ${name}`  // Template literal

// Boolean literals
true
false

// Object literal
{ name: "John", age: 30 }

// Array literal
[1, 2, 3, 4, 5]

// Regular expression literal
/pattern/flags

Next Steps

Now that you understand the basic syntax, let's explore variables and scope.