JavaScript Syntax

JavaScript Values

JavaScript syntax defines two types of values:

• Fixed values: Called literals (numbers, strings)
• Variable values: Called variables

JavaScript Literals

Numbers

10.50
1001

Strings

"Hello World"
'Hello World'

JavaScript Variables

Variables are used to store data values. JavaScript uses var, let, or const to declare variables:

let x;
x = 5;

JavaScript Operators

JavaScript uses arithmetic operators to compute values:

(5 + 6) * 10

JavaScript Expressions

An expression is a combination of values, variables, and operators, which computes to a value:

5 * 10
x * 10
"John" + " " + "Doe"

JavaScript Keywords

JavaScript keywords are reserved words that cannot be used as variable names:

• var, let, const - Declare variables
• if, else - Conditional statements
• for, while - Loops
• function - Define functions
• return - Return values

JavaScript Identifiers

Identifiers are names used to identify variables, functions, and objects. Rules:

• Can contain letters, digits, underscores, and dollar signs
• Must begin with a letter, underscore, or dollar sign
• Are case-sensitive
• Cannot use reserved words

JavaScript Comments

Comments are used to explain code and are ignored by JavaScript:

// This is a single-line comment

/*
This is a
multi-line comment
*/

JavaScript is Case Sensitive

JavaScript is case-sensitive. Variables lastName and lastname are different.

Camel Case

JavaScript programmers tend to use camel case for variable names:

let firstName = "John";
let lastName = "Doe";