JavaScript Syntax

JavaScript is a programming language. The Syntax rules define how the language is constructed.

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JavaScript Syntax

JavaScript is a scripting language. It is a lightweight, but powerful, programming language.

Syntax definition: "The principles by which sentences are constructed in a language."

The sentences of a programming language are called computer statements, or just statements.

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JavaScript Literals

In a programming language, literals are constant values like 3.14.

Number literals can be written with or without decimals, and with or without scientific notation (e):

3.14

1001

123e5

String literals can be written with double or single quotes:

"John Doe"

'John Doe'

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JavaScript Variables

In a programming language, variables are containers for storing information (data).

The equal sign (=) assigns a value to a named variable (just like in normal algebra):

x = 5

length = 6

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JavaScript Operators

 JavaScript uses operators to compute values (just like algebra):

5 + 6

a * b

 JavaScript can assign computed values to named variables (just like algebra):

x = 5 + 6

y = x * 10

Expressions like 5 + 6, and x * 10, are called expression literals.

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JavaScript Statements

In HTML, JavaScript statements are written as sequences of "commands" to the HTML browser.

Statements are separated by semicolons:

x = 5 + 6;
y = x * 10;

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JavaScript Keywords

A JavaScript statement often starts with a keyword. The var keyword tells the browser to create a new variable:

var x = 5 + 6;
var y = x * 10;

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JavaScript Comments

Not all JavaScript statements are "commands". Anything after double slashes // is ignored by the browser:

// I will not be executed

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JavaScript Data Types

JavaScript variables can hold many types of data: numbers, text strings, arrays, objects and much more:

var length = 16;                                      // Number assigned by a number literal
var lastName = "Johnson";                             // String assigned by a string literal
var cars = ["Saab", "Volvo", "BMW"];                  // Array  assigned by an array literal
var person = {firstName:John, lastName:Doe};          // Object assigned by an object literal

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JavaScript Functions

JavaScript statements written inside a function, can be invoked many times (reused):

Invoke a function = Call upon a function (ask for the code in the function to be executed).

function myFunction(a, b) {
    return a * b;                                     // returns the product of a and b
}

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JavaScript Identifiers

All programming languages must identify variables, functions, and objects, with unique names.

These unique names are called identifiers.

Identifier names can contain letters, digits, underscores, and dollar signs, but cannot begin with a number.

Reserved words (like JavaScript keywords) cannot be used as identifiers.

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JavaScript is Case Sensitive

In JavaScript all identifiers are case sensitive. 

The variables lastName and lastname, are two different variables.

The functions myFunction and myfunction, are two different functions.

JavaScript does not interpret Var; as var.

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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.

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