JavaScript Introduction
Javascript Can Change HTML Content
One of many JavaScript HTML methods is getElementById().
The example below "finds" an HTML element (with id="demo"), and changes the element content (innerHTML) to "Hello JavaScript":
Example
document.getelementById ("demo").innerHTML = "Hello JavaScript"
JavaScript accepts both double and single quotes:
Example
document.getelementById ('demo').innerHTML = 'Hello JavaScript'
Javascript Can Change HTML Styles(CSS)
Changing the style of an HTML element, is a variant of changing an HTML Attribute:
Example
document.getelementById ('demo').style.fontSize = "35px";
Javascript Can Hide HTML Elements
Hiding HTML elements can be done by changing the display style:
Example
document.getelementById ('demo').style.display = "none";
Javascript Can Show HTML Elements
Showing hidden HTML elements can also be done by changing the display style:
Example
document.getelementById ('demo').style.display = "block";
Did You Know?
JavaScript and Java are completely different languages, both in concept and design.
JavaScript was invented by Brendan Eich in 1995, and became an ECMA standard in 1997.
ECMA-262 is the official name of the standard. ECMAScript is the official name of the language.
JavaScript Syntax
JavaScript Values
The JavaScript syntax defines two types of values:
- Fixed values
- Variable values
Fixed values are called Literals.
Variable values are called Variables.
JavaScript Literals
The two most important syntax rules for fixed values are:
1.Numbers are written with or without decimals:
Example
10.50
1001
2.Strings are text, written within double or single quotes:
Example
"John Doe"
'John Doe'
JavaScript Variables
In a programming language, variables are used to store data values.
JavaScript uses the keywords var, let, and const to declare variables.
An equal sign is used to assign values to variables.
In this example, x is defined as a variable. Then, x is assigned (given) the value 6:
Example
let x;
x = 6;
JavaScript Operator
Javascript operators are used to perform different types of mathematical and logical computations.
Example
The Assignment Operator = assigns values
The Addition Operator + adds values
The Multiplication Operator * multiplies values
The Comparison Operator + compares values
JavaScript Assignment
The Assignment Operator (=) assigns a value to a variable:
Assignment Example
// Assign the value 5 to x
let x = 5;
// Assign the value 2 to y
let y = 2;
// Assign the value x + y to z:
let z = x + y;
JavaScript Arithmetics Operator
Arithmetic Operators are used to perform arithmetic on numbers:
Arithmetic Operator Example
let a = 3;
let x = (100 + 50) * a;
JavaScript Assignment Operator
Assignment operators assign values to JavaScript variables.
The Addition Assignment Operator (+=) adds a value to a variable.
Assignment
let x = 10;
x += 5;
JavaScript Comments
Not all JavaScript statements are "executed".
Code after double slashes
//or between/*and*/is treated as a comment.Comments are ignored, and will not be executed:
Example
let x; // I will be executed
// x = 6; I will NOT be executed