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

<script>
    //Write javascript code here...

</script>

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.

Variables

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

Example: JavaScript Statements

<script>
    var name = "Steve";
    id = 10;
</script>

Semicolon

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

Example: JavaScript Statements

<script>
    var one = 1, two = 2, three = 3; //three different statements
    
    var four = 4; //single statement
    var five = "Five"; //single statement without 
</script>

Whitespaces

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

Example: Whitespaces in JavaScript

<script>
    var one =1;
    var one   =   1;
    var one        =         1;
</script>

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

<script>
    var one =1; // this is a single line comment

    /* this  
    is multi line
    comment*/

    var two = 2;
    var three = 3;
</script>

String

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

Example: String in JavaScript

<script>
    var msg = "Hello World" //JavaScript string in double quotes
    
    var msg = 'Hello World' //JavaScript string in single quotes  
</script>

Number

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

 var name = prompt(“Enter your name:”, “John”);​if (name == null || name == "") {    document.getElementById(“msg”).innerHTML = “You did not entert anything. Please enter your name again”;}else{    document.getElementById(“msg”).innerHTML = “You enterted: ” + name;}javascript

<script>
    var num = 100;
    
    var float = 10.5;
</script>

Boolean

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

Example: Booleans in JavaScript

<script>
    var yes = true;
    
    var no = false;
</script>

Keywords

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.