Introduction to Javascript Basics

What is Javascript?

• It's a programming language used to make websites interactive.
• It can be written directly in a browser's console.
• To write Javascript code permanently, you need a code editor like Visual Studio Code.

Console.log

• This command is used to print a message to the browser's console.
• It's useful for debugging code and checking variable values.

Javascript Variables

• Variables are containers for storing data.
• They can store different data types:
  • Numbers: Used for numerical values (e.g., age, price).
  • Strings: Used for text (e.g., name, address).
  • Booleans: Used for true or false values (e.g., isFollowed).
  • Null: Represents the absence of a value.
  • Undefined: Indicates a variable hasn't been assigned a value.
  • BigInts: Used for very large integers.
  • Symbols: Unique identifiers.
• Variables must be declared with keywords:
  • let: Declares a variable that can be reassigned a different value.
  • const: Declares a variable with a constant value that cannot be reassigned.
  • var: An older way to declare variables, but it's not recommended because it has scoping issues.

Data Types

• Data types define the kind of data that can be stored in a variable.
• Javascript has two categories of data types:
  • Primitive Data Types: These are basic data types that hold a single value. There are seven primitive data types in Javascript.
  • Non-Primitive Data Types: These are more complex data types that can hold multiple values.
    • Objects: A collection of key-value pairs.

Operators

• Operators are used to perform operations on data.
• Javascript has several types of operators:
  • Arithmetic Operators: Perform mathematical operations (+, -, *, /, %, **).
    • Modulus Operator: Returns the remainder after division.
    • Exponentiation Operator: Raises a number to a power.
  • Assignment Operators: Assign values to variables ( =, +=, -=, *=, /=, %=, **=).
  • Comparison Operators: Compare values (==, !=, ===, !==, >, <, >=, <=).
    • Loose Equality (==): Checks if two values are equal, converting them to the same type if necessary.
    • Strict Equality (===): Checks if two values are equal and of the same data type.
    • Not Equal To (!=): Checks if two values are not equal, allowing type coercion.
    • Strict Not Equal To (!==): Checks if two values are not equal and of the same data type.
  • Logical Operators: Combine multiple expressions (&&, ||, !).
    • Logical AND (&&): Returns true if both expressions are true.
    • Logical OR (||): Returns true if at least one expression is true.
    • Logical NOT (!): Inverts the truthiness of an expression.

Conditional Statements

• Conditional statements control the flow of execution based on conditions.
• They allow you to make decisions within your code.
• Javascript has three main types of conditional statements:
  • if: Executes a block of code if the condition is true.
  • else if: Executes a block of code if the previous if conditions are false, but the current condition is true.
  • else: Executes a block of code if all preceding if and else if conditions are false.

Ternary Operator

• A shorthand way to write conditional expressions in a single line.
• Syntax: condition ? expression1 : expression2
  • If the condition is true, expression1 is evaluated and returned.
  • If the condition is false, expression2 is evaluated and returned.

Comments

• Comments are used to add explanations to your code without affecting its execution.
• Single-line comments: // This is a single-line comment
• Multi-line comments: /* This is a multi-line comment that can span multiple lines */

MDN Documentation

• MDN (Mozilla Developer Network) provides comprehensive documentation for web technologies, including Javascript.
• It's a valuable resource for learning new concepts, syntax, and best practices.

Loops

• Loops repeat a block of code multiple times.
• They're essential for automating repetitive tasks and working with data collections.
• Types of loops:
  • for: Executes a block of code a specific number of times.
  • while: Executes a block of code as long as a condition is true.
  • do while: Executes a block of code at least once, and then continues as long as a condition is true.
  • for...of: Iterates over each item in an iterable object, such as a string or array.
  • for...in: Iterates over each property of an object.

Infinite Loops

• An infinite loop runs indefinitely, which can cause problems by consuming resources.
• This usually happens when the loop's stopping condition is never met.
• It's important to ensure that loops have clear stopping conditions.

Arrays

• Arrays store collections of data.
• The elements of an array are ordered and can be accessed by their index, starting from 0.
• Array.length: Returns the number of elements in an array.
• Arrays are mutable, meaning their elements can be modified.

Array Methods

• Methods are functions associated with a specific object type (like an array).
• Common array methods:
  • push(): Adds one or more elements to the end of an array.
  • pop(): Removes the last element from an array and returns it.
  • unshift(): Adds one or more elements to the beginning of an array.
  • shift(): Removes the first element from an array and returns it.
  • slice(): Returns a shallow copy of a portion of the array.
  • splice(): Adds or removes elements from an array at a specific index.
  • concat(): Combines two or more arrays into a new array.
  • map(): Creates a new array by applying a function to each element of the original array.
  • filter(): Creates a new array containing only elements that satisfy a given condition.
  • reduce(): Applies a function to each element of an array, cumulatively building a single value.

Higher-Order Functions

• Functions that take other functions as arguments or return functions.
• Array.forEach(), Array.map(), Array.filter(), and Array.reduce() are examples of higher-order functions.

DOM (Document Object Model)

• The DOM is a programming interface for HTML documents.
• It represents an HTML document as a tree structure of nodes.
• Javascript can manipulate the DOM to change the content, style, and behavior of web pages dynamically.

Functions

• Functions are reusable blocks of code that perform specific tasks.
• They allow you to organize your code and avoid repetition.
• Function declaration:
  • function functionName(parameter1, parameter2) { ... }
• Function expression:
  • const functionName = function(parameter1, parameter2) { ... }
• Arrow functions:
  • const functionName = (parameter1, parameter2) => { ... }

Function Parameters

• Parameters are variables that a function accepts as input.
• They're defined within the function's parentheses.

Function Arguments

• Arguments are the values that are passed to a function when it's called.

Function Return Value

• A function can return a value using the return keyword.
• The returned value can be used in other parts of the code.

Scoping

• The scope of a variable determines where it can be accessed within the code.
• Variables declared inside a function are local to that function.

The Three Pillars of Front-End Development

• HTML (HyperText Markup Language): Defines the structure and content of a web page.
• CSS (Cascading Style Sheets): Controls the visual appearance and layout of a web page.
• Javascript: Adds interactivity and dynamic behavior to a web page.

Basic Styling in HTML5 and CSS

• We can add styles to HTML elements using CSS (Cascading Style Sheets).
• CSS is used to control the layout and appearance of HTML elements.
• We can add CSS styles directly to an HTML element using the style attribute.
• Example: Heading - This will make the heading blue.

Connecting CSS to HTML

• To connect an external CSS file to an HTML file, we use the `` tag.
• The `` tag is used to link an external stylesheet to an HTML document.
• Example: `` - This links the style.css file to the HTML document.

CSS Properties and Values

• We can define styles using CSS properties and values.
• Property: The aspect of the element we want to style (e.g. color, background-color, font-size, etc.).
• Value: The specific value we want to assign to the property (e.g. blue, pink, 16px, etc.).
• Example: color: blue; - This sets the text color to blue.

CSS Selectors

• We can target specific HTML elements using CSS selectors.
• Example: h1 { color: blue; } - This targets all `` elements and sets their text color to blue.

JavaScript and HTML

• We can add JavaScript code to an HTML file using the `` - This links the script.js file to the HTML document.

The Window Object

• The Window object is a global object in JavaScript that represents the browser window.
• We can access the Window object using the window keyword.
• The Window object has many properties and methods that we can use to interact with the browser window.
• Example: window.alert("Hello, World!"); - This will display an alert box with the message "Hello, World!".

Inspecting HTML Elements

• We can inspect HTML elements using the browser's developer tools.
• The Elements tab in the developer tools allows us to view the HTML structure of the page and inspect individual elements.
• We can use the Styles tab to view the CSS styles applied to an element.
• We can use the Console tab to execute JavaScript code and interact with the page.Here are the study notes for the provided text:

Understanding the Window Object

• The Window object is a global object that is available everywhere in JavaScript.
• It represents the browser's window and is the topmost object in the JavaScript hierarchy.
• The Window object has many properties and methods that can be accessed directly, such as window.alert() or window.prompt().
• The Window object also has a property called document, which is an object representing the HTML document.

Understanding the Document Object

• The Document object represents the HTML document and is a property of the Window object.
• The Document object has many properties and methods that can be accessed directly, such as document.write() or document.body.
• The Document object has a property called body, which represents the body of the HTML document.

Understanding the DOM (Document Object Model)

• The DOM is a tree-like structure that represents the HTML document.
• Each node in the DOM represents an element in the HTML document, such as a heading, paragraph, or button.
• The DOM is dynamic, meaning it can be modified by JavaScript code.
• The DOM can be accessed and manipulated using JavaScript, allowing developers to create interactive web pages.

Understanding the role of JavaScript in the DOM

• JavaScript can be used to manipulate the DOM, allowing developers to dynamically change the content and structure of the HTML document.
• JavaScript code can be executed when a user interacts with the web page, such as when a button is clicked.
• JavaScript code can also be executed when the HTML document is loaded, allowing developers to initialize the page with dynamic content.

Understanding Dynamic Changes in the DOM

• Dynamic changes in the DOM refer to changes made to the HTML document structure or content using JavaScript code.
• Dynamic changes can be made to the DOM when a user interacts with the web page, such as when a button is clicked.
• Dynamic changes can also be made to the DOM when the HTML document is loaded, allowing developers to initialize the page with dynamic content.

Understanding the importance of DOM Manipulation

• DOM manipulation is essential for creating interactive web pages that respond to user input.
• DOM manipulation allows developers to dynamically change the content and structure of the HTML document, creating a more engaging user experience.
• DOM manipulation is also important for web page optimization, as it allows developers to dynamically load and unload content, reducing the page's load time.

What is Javascript?

• Javascript is a programming language used to make websites interactive
• It can be written directly in a browser's console or permanently in a code editor like Visual Studio Code

Console.log

• Console.log is a command used to print a message to the browser's console
• It's useful for debugging code and checking variable values

Javascript Variables

• Variables are containers for storing data
• They can store different data types, including:
  • Numbers (numerical values, e.g., age, price)
  • Strings (text, e.g., name, address)
  • Booleans (true or false values, e.g., isFollowed)
  • Null (represents the absence of a value)
  • Undefined (indicates a variable hasn't been assigned a value)
  • BigInts (very large integers)
  • Symbols (unique identifiers)
• Variables must be declared with keywords, including:
  • let (declares a variable that can be reassigned a different value)
  • const (declares a variable with a constant value that cannot be reassigned)
  • var (an older way to declare variables, but not recommended due to scoping issues)

Data Types

• Data types define the kind of data that can be stored in a variable
• Javascript has two categories of data types:
  • Primitive Data Types (basic data types that hold a single value)
  • Non-Primitive Data Types (more complex data types that can hold multiple values)
• Examples of primitive data types include Objects (a collection of key-value pairs)

Operators

• Operators are used to perform operations on data
• Types of operators include:
  • Arithmetic Operators (perform mathematical operations, e.g., +, -, *, /, %)
  • Modulus Operator (returns the remainder after division)
  • Exponentiation Operator (raises a number to a power)
  • Assignment Operators (assign values to variables, e.g., =, +=, -=, *=, /=, %=, **=)
  • Comparison Operators (compare values, e.g., ==, !=, ===, !==, >, =, <=)

Functions

• Parameters are variables that a function accepts as input
• They're defined within the function's parentheses
• Arguments are the values that are passed to a function when it's called
• A function can return a value using the return keyword
• The returned value can be used in other parts of the code

Scoping

• The scope of a variable determines where it can be accessed within the code
• Variables declared inside a function are local to that function

The Three Pillars of Front-End Development

• HTML defines the structure and content of a web page
• CSS controls the visual appearance and layout of a web page
• Javascript adds interactivity and dynamic behavior to a web page

Basic Styling in HTML5 and CSS

• We can add styles to HTML elements using CSS
• CSS is used to control the layout and appearance of HTML elements
• We can add CSS styles directly to an HTML element using the style attribute

Connecting CSS to HTML

• To connect an external CSS file to an HTML file, we use the `` tag
• The `` tag is used to link an external stylesheet to an HTML document

CSS Properties and Values

• We can define styles using CSS properties and values
• Property: The aspect of the element we want to style (e.g., color, background-color, font-size, etc.)
• Value: The specific value we want to assign to the property (e.g., blue, pink, 16px, etc.)

CSS Selectors

• We can target specific HTML elements using CSS selectors
• Example: h1 { color: blue; } targets all `` elements and sets their text color to blue

Learn the fundamentals of Javascript, including its use in making websites interactive, writing code in the browser's console, and variables for storing data.