JavaScript Can Change HTML Content
One of many JavaScript HTML methods is getElementById().avaScript was initially created to “make web pages alive”.
The programs in this language are called scripts. They can be written right in a web page’s HTML and run automatically as the page loads.
Scripts are provided and executed as plain text. They don’t need special preparation or compilation to run.
In this aspect, JavaScript is very different from another language called Java.
JavaScript is a scripting or programming language that allows you to implement complex features on web pages — every time a web page does more than just sit there and display static
information for you to look at — displaying timely content updates, interactive maps, animated 2D/3D graphics,
scrolling video jukeboxes, etc. — you can bet that JavaScript is probably involved.
It is the third layer of the layer cake of standard web technologies,
two of which (HTML and CSS) we have covered in much more detail in other parts of the Learning Area.
HTML is the markup language that we use to structure and give meaning to our web content, for example defining paragraphs, headings, and data tables, or embedding images and videos in the page.
CSS is a language of style rules that we use to apply styling to our HTML content, for example setting background colors and fonts, and laying out our content in multiple columns.
JavaScript is a scripting language that enables you to create dynamically updating content, control multimedia,
animate images, and pretty much everything else.
(Okay, not everything, but it is amazing what you can achieve with a few lines of JavaScript code.)
JavaScript Variables and Data type
Variables are Containers for Storing Data
JavaScript Variables can be declared in 4 ways:
Automatically
Using var
Using let
Using const
In this first example, x, y, and z are undeclared variables.
x = 5;
y = 6;
z = x + y;
Data type
JavaScript has 8 Datatypes:-
String
Number
Bigint
Boolean
Undefined
Null
Symbol
Object
The Object Datatype
The object data type can contain both built-in objects, and user defined objects:
Built-in object types can be:
objects, arrays, dates, maps, sets, intarrays, floatarrays, promises, and more.
The Concept of Data Types
In programming, data types is an important concept.
To be able to operate on variables, it is important to know something about the type.
Without data types, a computer cannot safely solve this:
let x = 16 + "Volvo";
Refers the following video for a guidence:
JavaScript Comment
Single Line Comments:- Single line comments start with //.
Any text between // and the end of the line will be ignored by JavaScript (will not be executed).
This example uses a single-line comment before each code line:
Example:-
// Change heading:
document.getElementById("myH").innerHTML = "My First Page";
// Change paragraph:
document.getElementById("myP").innerHTML = "My first paragraph.";
This example uses a single line comment at the end of each line to explain the code:
Example
let x = 5; // Declare x, give it the value of 5
let y = x + 2; // Declare y, give it the value of x + 2
Multi-line:- Multi-line comments start with /* and end with */.
Any text between /* and */ will be ignored by JavaScript.
This example uses a multi-line comment (a comment block) to explain the code:
Example
/*
The code below will change
the heading with id = "myH"
and the paragraph with id = "myP"
in my web page:
*/
document.getElementById("myH").innerHTML = "My First Page";
document.getElementById("myP").innerHTML = "My first paragraph.";
JavaScript operaters
For more knowledge refers the following link:-Link
JavaScript
