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";
Note: JavaScript keywords are case-sensitive. JavaScript does not interpret LET or Let as the keyword let.
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.
Note: Hyphens are not allowed in JavaScript. They are reserved for subtractions.
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.
Note: JavaScript programmers tend to use lower camel case.
