JavaScript Notes Revision Part 1

JavaScript
JavaScript is a powerful programming language that can add interactivity to a website. It was invented by Brendan Eich.
Functions
Functions are a way of packaging functionality that you wish to reuse. It's possible to define a body of code as a function that executes when you call the function name in your code. This is a good alternative to repeatedly writing the same code. You have already seen some uses of functions. For example:
let myVariable = document.querySelector("h1");
alert("hello!"); //buit-into browser JavaScript functions
Return statement
The return statement ends function execution and specifies a value to be returned to the function caller.
JS Events
HTML events are "things" that happen to HTML elements. When JavaScript is used in HTML pages, JavaScript can "react" on these events.
OnMouseOver
The user moves the mouse over an HTML element
OnCLick
The user clicks an HTML element
Objects
In JavaScript,almost "everything" is an object. All JavaScript values, except primitives, are objects.
Objects in JavaScript, just as in many other programming languages, can be compared to objects in real life. In JavaScript, an object is a standalone entity, with properties and type. Compare it with a cup, for example. A cup is an object, with properties. A cup has a color, a design, weight, a material it is made of, etc. The same way, JavaScript objects can have properties, which define their characteristics.
A javaScript object is an entity having state and behavior (properties and method). For example: car, pen, bike, chair, glass, keyboard, monitor etc. JavaScript is an object-based language. Everything is an object in JavaScript. JavaScript is template based not class based. Here, we don't create class to get the object. But, we direct create objects.
Math functions in JavaScript
The JavaScript Math object allows you to perform mathematical tasks on numbers.
The syntax for any Math property is : Math.property.
The syntax for any Math methods is : Math.method(number)
Math is a built-in object that has properties and methods for mathematical constants and functions. It's not a function object. Math works with the Number type.
Arrays and Array Functions in JavaScript
The Array object is used to store multiple values in a single variable. JavaScript Array Methods.