[04] JavaScript Syntax

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 semicolons.

 

<p id="demo"></p> <script>   var x = 5;   var y = 6;   var z = x + y;   document.getElementById("demo").innerHTML = z; </script>

	In HTML, JavaScript programs can be executed by the web browser.

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 calledvariables.

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JavaScript Literals

The most important rules for writing fixed values are:

Numbers are written with or without decimals: 0.01, 1000

Strings are text, written within double or single quotes: "John Doe", 'John Doe'

Expressions can also represent fixed values: 5 + 6, 5 * 10

 

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.

Thevar keyword tells the browser to create a new variable:

<p id="demo"></p> <script>    var x = 5 + 6;    var y = x * 10;    document.getElementById("demo").innerHTML = y; </script>

 

 

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:

 

<p id="demo"></p> <script>   var x = 5;   // var x = 6; I will not be executed   document.getElementById("demo").innerHTML = x; </script>

 

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.

JavaScript Character Set

JavaScript uses the Unicode character set.

Unicode covers (almost) all the characters, punctuations, and symbols in the world.

For a closer look, please study our Complete Unicode Reference.