Functions in Programming

Functions

• A block of code that can be executed multiple times from different parts of a program
• Can take arguments, which are values passed to the function when it's called
• Can return values, which can be used by the code that called the function
• Can be defined with a name, or anonymously
• Types of functions:
  • Function declaration: function name(parameters) { code }
  • Function expression: const name = function(parameters) { code }
  • Arrow function: const name = (parameters) => { code }
• Function scope: variables defined inside a function are only accessible within that function
• Hoisting: function declarations are moved to the top of their scope, allowing them to be called before they're defined

Arrays

• A data structure that stores a collection of values
• Values can be of any type, including strings, numbers, and objects
• Indexed, meaning each value has a unique index or key
• Can be created using the [] syntax or the Array constructor
• Methods:
  • push(): adds one or more values to the end of the array
  • pop(): removes the last value from the array and returns it
  • shift(): removes the first value from the array and returns it
  • unshift(): adds one or more values to the beginning of the array
  • splice(): adds or removes values from a specific position in the array
  • indexOf(): returns the index of the first occurrence of a value in the array
  • includes(): returns a boolean indicating whether a value is in the array
• Array manipulation:
  • Concatenation: combining two or more arrays using the spread operator (...)
  • Slicing: creating a new array from a subset of an existing array using the slice() method
  • Mapping: creating a new array by applying a function to each value in an existing array using the map() method
  • Filtering: creating a new array by selecting values from an existing array that meet a certain condition using the filter() method
  • Reducing: reducing an array to a single value by applying a function to each value using the reduce() method

Functions

• A block of code that can be executed multiple times from different parts of a program, allowing for code reuse and modularity.
• Functions can take arguments, which are values passed to the function when it's called, and use them to perform calculations or operations.
• Functions can also return values, which can be used by the code that called the function, allowing for more complex logic and data flow.
• Functions can be defined with a name, or anonymously, and can be assigned to variables or passed as arguments to other functions.
• There are three types of function definitions: function declaration, function expression, and arrow function, each with its own syntax and use cases.

Arrays

• A data structure that stores a collection of values, which can be of any type, including strings, numbers, and objects.
• Arrays are indexed, meaning each value has a unique index or key, allowing for efficient access and manipulation.
• Arrays can be created using the [] syntax or the Array constructor, and can be manipulated using various methods.
• Array methods include:
  • push(): adds one or more values to the end of the array.
  • pop(): removes the last value from the array and returns it.
  • shift(): removes the first value from the array and returns it.
  • unshift(): adds one or more values to the beginning of the array.
  • splice(): adds or removes values from a specific position in the array.
  • indexOf(): returns the index of the first occurrence of a value in the array.
  • includes(): returns a boolean indicating whether a value is in the array.
• Arrays can be manipulated using various techniques, including:
  • Concatenation: combining two or more arrays using the spread operator (...).
  • Slicing: creating a new array from a subset of an existing array using the slice() method.
  • Mapping: creating a new array by applying a function to each value in an existing array using the map() method.
  • Filtering: creating a new array by selecting values from an existing array that meet a certain condition using the filter() method.
  • Reducing: reducing an array to a single value by applying a function to each value using the reduce() method.

Variables

• Variables are declared using the let, const, and var keywords.
• JavaScript has two main types of variables: Primitive and Reference.
• Primitive types include number, string, boolean, null, undefined, and symbol.
• Reference types include object, array, and function.
• Variables have a scope, which determines their accessibility.
• Global variables are declared outside a function or block scope.
• Local variables are declared inside a function or block scope.
• Variables declared with var are "hoisted" to the top of their scope.
• Variables declared with let and const are not "hoisted".

Functions

• Functions are declared using the function keyword.
• There are two main types of functions: Function Declaration and Function Expression.
• Function Declaration is a function declared as a separate statement.
• Function Expression is a function declared as an expression, often assigned to a variable.
• Functions can take arguments, which are passed when the function is called.
• Functions can return a value using the return statement.
• A function has access to its own scope and the scope of its parent functions, creating a closure.
• Arrow Functions are a concise way to declare functions, introduced in ECMAScript 6 (ES6).

Object-Oriented Programming (OOP)

• Objects are collections of key-value pairs, created using the {} syntax.
• Properties are the key-value pairs within an object.
• Methods are functions within an object, used to perform actions on the object.
• Inheritance is the process of creating a new object based on an existing object, using the prototype chain.
• Constructors are special functions used to create new objects, often with the new keyword.
• Prototypes are objects that serve as a blueprint for other objects, allowing for inheritance and method sharing.
• The this keyword refers to the current object being executed, often used in methods and constructors.