JavaScript Syntax

JavaScript syntax is the set of rules, how JavaScript programs are constructed.

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JavaScript Programs

A computer program is a list of "instructions" to be "executed" by the computer.
In a programming language, these program instructions are called statements.
JavaScript is a programming language.
JavaScript statements are separated by semicolon.

Example

var x = 5;
var y = 6;
var z = x + y;

JavaScript Statements

JavaScript statements are composed of:
Values, Operators, Expressions, Keywords, and Comments.

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JavaScript Values

The JavaScript syntax defines two types of values: Fixed values and variable values.
Fixed values are called literals. Variable values are called variables.

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JavaScript Literals

The most important rules for writing fixed values are:
Numbers are written with or without decimals:

10.50

1001

 

Strings are text, written within double or single quotes:

"John Doe"

'John Doe' 

 

JavaScript Variables

In a programming language, variables are used to store data values.
JavaScript uses the var keyword to define variables.
An equal sign is used to assign values to variables.
In this example, x is defined as a variable. Then, x is assigned (given) the value 6:

var x;

x = 6; 

 

JavaScript Operators

JavaScript uses an assignment operator ( = ) to assign values to variables:

var x = 5;
var y = 6;

 

JavaScript uses arithmetic operators ( + - *  / ) to compute values:
(5 + 6) * 10

 

JavaScript Keywords

JavaScript keywords are used to identify actions to be performed.
The var keyword tells the browser to create a new variable:

var x = 5 + 6;
var y = x * 10; 

 

JavaScript Comments

Not all JavaScript statements are "executed".
Code after double slashes // or between /* and */ is treated as a comment.
Comments are ignored, and will not be executed:

var x = 5;   // I will be executed
// var x = 6;   I will NOT be executed

  

JavaScript is Case Sensitive

All JavaScript identifiers are case sensitive. 
The variables lastName and lastname, are two different variables.

lastName = "Doe";
lastname = "Peterson"; 

 

JavaScript does not interpret VAR or Var as the keyword var.

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JavaScript and Camel Case

Historically, programmers have used three 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.
Camel Case:
FirstName, LastName, MasterCard, InterCity.

In programming languages, especially in JavaScript, camel case often starts with a lowercase letter:
firstName, lastName, masterCard, interCity.

	Hyphens are not allowed in JavaScript. It is reserved for subtractions.