Syntax Rules
// How to Declare variables:
let x = 5;
let y = 6;
// How to Compute values:
let z = x + y;
// I am a Comment. I do NothingJavaScript 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:
10.50
1001Strings are text, written within double or single quotes:
"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 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:
5 * 10JavaScript Expressions
An expression is a combination of values, variables, and operators, which computes to a value.
(5 + 6) * 10JavaScript 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.
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. JavaScript programmers tend to use lower camel case. Video: JavaScript Syntax
Lower Camel Case
firstName, lastName, masterCard, interCity.
JavaScript programmers tend to use lower camel case.