Content

• JavaScript Introduction
• Where to write JS
• JavaScript Output
• JavaScript Statements
• JavaScript Syntax
• JavaScript Comments

JavaScript Introduction

• JavaScript is mainly used to program the behavior of web pages
• Using JavaScript, we can change and update HTML and CSS.
• Javascript frameworks (e.g. - node.js) also can be used to develop dynamic web applications.
• There are various JS stacks available for full stack Development

• JavaScript can be use to implement Web API, Web forms API etc.

Where to write JS

• In HTML, JavaScript code is inserted between <script> and </script> tags.
• We can create separate JavaScript file (extension - .js)
• We use <script> tag to give external Javascript reference in HTML page

Example

Output:

Code:

<p id="demo"></p>

<script>
document.getElementById("demo").innerHTML = "My text comes from Javascript";
</script>

JavaScript Output

JavaScript can display output in different ways as listed below

• Output into an HTML element, using innerHTML
• Output into the HTML document using document.write()
• Output into an alert box, using alert()
• Output into the browser console, using console.log()

JavaScript Statements

• In a programming language, these programming instructions are called statements.
• A JavaScript program is a list of programming statements.
• In HTML, JavaScript programs are executed by the web browser.
• JavaScript statements are composed of Values, Operators, Expressions, Keywords, and Comments
• The statements are executed, one by one, in the same order as they are written.
• Semicolons separate JavaScript statements.

Example : JavaScript Statements

let a, b, c;  // Declare 3 variables
a = 5;        // Assign the value 5 to a
b = 6;        // Assign the value 6 to b
c = a + b;    // Assign the sum of a and b to c

JavaScript Syntax

• JavaScript syntax is the set of rules, how JavaScript programs are constructed.
• Variable values are called Variables.
• Strings are text, written within double or single quotes
• In a programming language, variables are used to store data values
• JavaScript uses arithmetic operators ( + - * / ) to compute values
• JavaScript uses an assignment operator ( = ) to assign values to variables

JavaScript Comments

• JavaScript comments can be used to explain JavaScript code, and to make it more readable.
• JavaScript comments can also be used to prevent execution, when testing alternative code.
• Code after double slashes // or between /* and */ is treated as a comment.

Example

Single Line Comments

<script>
// Below code will change content of html tag whose id is heading1:
document.getElementById("heading1").innerHTML = "JavaScript Comments";
</script>

Multi-line Comments

<script>
/*
The code below will change
the heading with id = "myH"
and the paragraph with id = "myP"
*/
document.getElementById("myH").innerHTML = "JavaScript Comments";
document.getElementById("myP").innerHTML = "My first paragraph.";
</script>