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codingquill · 1 year ago

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JavaScript Fundamentals

I have recently completed a course that extensively covered the foundational principles of JavaScript, and I'm here to provide you with a concise overview. This post will enable you to grasp the fundamental concepts without the need to enroll in the course.

Prerequisites: Fundamental HTML Comprehension

Before delving into JavaScript, it is imperative to possess a basic understanding of HTML. Knowledge of CSS, while beneficial, is not mandatory, as it primarily pertains to the visual aspects of web pages.

Manipulating HTML Text with JavaScript

When it comes to modifying text using JavaScript, the innerHTML function is the go-to tool. Let's break down the process step by step:

Initiate the process by selecting the HTML element whose text you intend to modify. This selection can be accomplished by employing various DOM (Document Object Model) element selection methods offered by JavaScript ( I'll talk about them in a second )

Optionally, you can store the selected element in a variable (we'll get into variables shortly).

Employ the innerHTML function to substitute the existing text with your desired content.

Element Selection: IDs or Classes

You have the opportunity to enhance your element selection by assigning either an ID or a class:

Assigning an ID:

To uniquely identify an element, the .getElementById() function is your go-to choice. Here's an example in HTML and JavaScript:

HTML:

<button id="btnSearch">Search</button>

JavaScript:

document.getElementById("btnSearch").innerHTML = "Not working";

This code snippet will alter the text within the button from "Search" to "Not working."

Assigning a Class:

For broader selections of elements, you can assign a class and use the .querySelector() function. Keep in mind that this method can select multiple elements, in contrast to .getElementById(), which typically focuses on a single element and is more commonly used.

Variables

Let's keep it simple: What's a variable? Well, think of it as a container where you can put different things—these things could be numbers, words, characters, or even true/false values. These various types of stuff that you can store in a variable are called DATA TYPES.

Now, some programming languages are pretty strict about mentioning these data types. Take C and C++, for instance; they're what we call "Typed" languages, and they really care about knowing the data type.

But here's where JavaScript stands out: When you create a variable in JavaScript, you don't have to specify its data type or anything like that. JavaScript is pretty laid-back when it comes to data types.

So, how do you make a variable in JavaScript?

There are three main keywords you need to know: var, let, and const.

But if you're just starting out, here's what you need to know :

const: Use this when you want your variable to stay the same, not change. It's like a constant, as the name suggests.

var and let: These are the ones you use when you're planning to change the value stored in the variable as your program runs.

Note that var is rarely used nowadays

Check this out:

let Variable1 = 3; var Variable2 = "This is a string"; const Variable3 = true;

Notice how we can store all sorts of stuff without worrying about declaring their types in JavaScript. It's one of the reasons JavaScript is a popular choice for beginners.

Arrays

Arrays are a basically just a group of variables stored in one container ( A container is what ? a variable , So an array is also just a variable ) , now again since JavaScript is easy with datatypes it is not considered an error to store variables of different datatypeslet

for example :

myArray = [1 , 2, 4 , "Name"];

Objects in JavaScript

Objects play a significant role, especially in the world of OOP : object-oriented programming (which we'll talk about in another post). For now, let's focus on understanding what objects are and how they mirror real-world objects.

In our everyday world, objects possess characteristics or properties. Take a car, for instance; it boasts attributes like its color, speed rate, and make.

So, how do we represent a car in JavaScript? A regular variable won't quite cut it, and neither will an array. The answer lies in using an object.

const Car = { color: "red", speedRate: "200km", make: "Range Rover" };

In this example, we've encapsulated the car's properties within an object called Car. This structure is not only intuitive but also aligns with how real-world objects are conceptualized and represented in JavaScript.

Variable Scope

There are three variable scopes : global scope, local scope, and function scope. Let's break it down in plain terms.

Global Scope: Think of global scope as the wild west of variables. When you declare a variable here, it's like planting a flag that says, "I'm available everywhere in the code!" No need for any special enclosures or curly braces.

Local Scope: Picture local scope as a cozy room with its own rules. When you create a variable inside a pair of curly braces, like this:

//Not here { const Variable1 = true; //Variable1 can only be used here } //Neither here

Variable1 becomes a room-bound secret. You can't use it anywhere else in the code

Function Scope: When you declare a variable inside a function (don't worry, we'll cover functions soon), it's a member of an exclusive group. This means you can only name-drop it within that function. .

So, variable scope is all about where you place your variables and where they're allowed to be used.

Adding in user input

To capture user input in JavaScript, you can use various methods and techniques depending on the context, such as web forms, text fields, or command-line interfaces.We’ll only talk for now about HTML forms

HTML Forms:

You can create HTML forms using the <;form> element and capture user input using various input elements like text fields, radio buttons, checkboxes, and more.

JavaScript can then be used to access and process the user's input.

Functions in JavaScript

Think of a function as a helpful individual with a specific task. Whenever you need that task performed in your code, you simply call upon this capable "person" to get the job done.

Declaring a Function: Declaring a function is straightforward. You define it like this:

function functionName() { // The code that defines what the function does goes here }

Then, when you need the function to carry out its task, you call it by name:

functionName();

Using Functions in HTML: Functions are often used in HTML to handle events. But what exactly is an event? It's when a user interacts with something on a web page, like clicking a button, following a link, or interacting with an image.

Event Handling: JavaScript helps us determine what should happen when a user interacts with elements on a webpage. Here's how you might use it:

HTML:

<button onclick="FunctionName()" id="btnEvent">Click me</button>

JavaScript:

function FunctionName() { var toHandle = document.getElementById("btnEvent"); // Once I've identified my button, I can specify how to handle the click event here }

In this example, when the user clicks the "Click me" button, the JavaScript function FunctionName() is called, and you can specify how to handle that event within the function.

Arrow functions : is a type of functions that was introduced in ES6, you can read more about it in the link below

If Statements

These simple constructs come into play in your code, no matter how advanced your projects become.

If Statements Demystified: Let's break it down. "If" is precisely what it sounds like: if something holds true, then do something. You define a condition within parentheses, and if that condition evaluates to true, the code enclosed in curly braces executes.

If statements are your go-to tool for handling various scenarios, including error management, addressing specific cases, and more.

Writing an If Statement:

if (Variable === "help") { console.log("Send help"); // The console.log() function outputs information to the console }

In this example, if the condition inside the parentheses (in this case, checking if the Variable is equal to "help") is true, the code within the curly braces gets executed.

Else and Else If Statements

Else: When the "if" condition is not met, the "else" part kicks in. It serves as a safety net, ensuring your program doesn't break and allowing you to specify what should happen in such cases.

Else If: Now, what if you need to check for a particular condition within a series of possibilities? That's where "else if" steps in. It allows you to examine and handle specific cases that require unique treatment.

Styling Elements with JavaScript

This is the beginner-friendly approach to changing the style of elements in JavaScript. It involves selecting an element using its ID or class, then making use of the .style.property method to set the desired styling property.

Example:

Let's say you have an HTML button with the ID "myButton," and you want to change its background color to red using JavaScript. Here's how you can do it:

HTML: <button id="myButton">Click me</button>

JavaScript:

// Select the button element by its ID const buttonElement = document.getElementById("myButton"); // Change the background color property buttonElement.style.backgroundColor = "red";

In this example, we first select the button element by its ID using document.getElementById("myButton"). Then, we use .style.backgroundColor to set the background color property of the button to "red." This straightforward approach allows you to dynamically change the style of HTML elements using JavaScript.

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learnershub101 · 1 year ago

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