JavaScript Syntax

Syntax Rules

Syntax are the rules how programs must be constructed:

// How to Declare variables: let x = 5; let y = 6;

// How to Compute values: let z = x + y;

// I am a Comment. I do Nothing

JavaScript Values

The JavaScript syntax defines two types of values:

• Literals (Fixed values)
• Variables (Variable values)

JavaScript Literals

The most important syntax rules for literals (fixed values) are:

Numbers are written with or without decimals:

Example

10.50

1001

Strings are text, written within double or single quotes:

Example

"John Doe"

'John Doe'

JavaScript Keywords

JavaScript keywords are used to defines actions to be performed.

The let and const keywords create variables:

Example

let x = 5;

const fname = "John";

JavaScript Variables

Variables are containers for storing data values.

Variables must be identified with unique names.

Example

// Define x as a variable

let x;

// Assign the value 6 to x

x = 6;

JavaScript Identifiers

An identifier is the name you give to a variable.

Rules for identifiers:

• Must start with a letter, _, or $
• Can contain digits after the first character
• Cannot be a reserved keyword (let, const, if, etc.)
• Are case-sensitive

JavaScript Operators

JavaScript assignment operators (=) assign values to variables:

Example

let x = 5;

let y = 6;

let sum = x + y;

JavaScript uses arithmetic operators ( + - * / ) to compute values:

Example

5 * 10

JavaScript Expressions

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

Examples

(5 + 6) * 10

JavaScript is Case Sensitive

JavaScript identifiers are case sensitive.

The variables lastName and lastname, are different variables:

Example

let lastName = "Doe";

let lastname = "Peterson";

JavaScript and Camel Case

Historically, programmers have used different ways of joining multiple words into one variable name:

Hyphens:

first-name, last-name, master-card, inter-city.

Underscore:

first_name, last_name, master_card, inter_city.

Upper Camel Case (Pascal Case):

FirstName, LastName, MasterCard, InterCity.

Lower Camel Case:

firstName, lastName, masterCard, interCity.

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