JavaScript Syntax

Learn some important characteristics of JavaScript syntax in this section.

As mentioned in the previous chapter, JavaScript code can be written inside HTML Script Tags or in a separate file with .js extension.

Write JavaScript Code
    //Write javascript code here...


Character Set

JavaScript uses the unicode character set, so allows almost all characters, punctuations, and symbols.

Case Sensitive

JavaScript is a case-sensitive scripting language. So, name of functions, variables and keywords are case sensitive. For example, myfunction and MyFunction are different, Name is not equal to nAme, etc.


In JavaScript, a variable is declared with or without the var keyword.

Example: JavaScript Statements
    var name = "Steve";
    id = 10;


JavaScript statements are separated by a semicolon. However, it is not mandatory to end a statement with a semicolon, but it is recommended.

Example: JavaScript Statements
    var one = 1; two = 2; three = 3; //three different statements
    var four = 4; //single statement
    var five = "Five" //single statement without ;


JavaScript ignores multiple spaces and tabs. The following statements are the same.

Example: Whitespaces in JavaScript
    var one =1;
    var one   =   1;
    var one        =         1;

Code Comments

A comment is single or multiple lines, which give some information about the current program. Comments are not for execution.

Write comment after double slashes // or write multiple lines of comments between /* and */

Example: Comment JavaScript Code
    var one =1; // this is a single line comment

    /* this  
    is multi line

    var two = 2;
    var three = 3;


A string is a text in JavaScript. The text content must be enclosed in double or single quotation marks.

Example: String in JavaScript
    var msg = "Hello World" //JavaScript string in double quotes
    var msg = 'Hello World' //JavaScript string in single quotes  


JavaScript allows you to work with any type of number like integer, float, hexadecimal etc. Number must NOT be wrapped in quotation marks.

Example: Numbers in JavaScript
    var num = 100;
    var flot = 10.5;


As in other languages, JavaScript also includes true and false as a boolean value.

Example: Booleans in JavaScript
    var yes = true;
    var no = false;


Keywords are reserved words in JavaScript, which cannot be used as variable names or function names.

The following table lists some of the keywords used in JavaScript.

JavaScript Reserved Keywords
var function if
else do while
for switch break
continue return try
catch finally debugger
case class this
default false true
in instanceOf typeOf
new null throw
void width delete
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