JavaScript Functions Introduction

Functions Intro

• Functions are reusable code blocks that encapsulate multiple statements, expressions, and logics into a single unit.
• They prevent redundancy in code and can be used to create mini programs inside a larger program.
• Functions are classified as objects in JavaScript and can be made to run in the context of other functions or objects.

Function Declaration

• Function declaration is a syntax that uses the keyword function followed by the function name and the code block inside curly braces.
• Syntax: function functionName(parameters) { code block }
• Data passed into a function is called arguments and can accept all data types, including primitive and non-primitive data types, as well as other functions known as callback functions.
• Code block is denoted by curly braces and contains the logic of the function.
• Function declaration in JavaScript is hoisted to the global scope, which means it can be used before it is declared.

Function Expression

• Function expressions are similar to function declarations but are assigned to a variable.
• A function without a name is called an anonymous function.
• The major difference between function expressions and function declarations is that function expressions are not hoisted to the top of the global scope.
• Function expressions can be used to assign default values to parameters using the nullish coalescing operator.

This Keyword

• The this keyword refers to the object that the function is a property of.
• In a web browser, the this keyword points to the global window object outside a function.
• Inside a function, the this keyword may point to the global scope if use strict is not used.
• If the this keyword is used in an object, it points to the object that the function is a property of and allows us to access the object's properties, methods, and values.

Function Call and Bind Methods

• The call method can be used to invoke a function with an owner object as an argument.
• The bind method creates a new function that, when called, has its this keyword set to the provided value.
• The difference between call and bind is that call invokes the function immediately, while bind returns a new function that can be invoked later for reusability.

Arrow Functions

• Arrow functions are anonymous functions that can be assigned to constants and variables.
• Arrow functions can be written both declaratively and as expressions.
• Arrow functions let you return an expression without using the return keyword or curly braces.
• Arrow functions do not create a context of their own and instead inherit the context of the parent function.

Constructor Functions

• Constructor functions are used to create multiple instances of an object with the same properties and methods.
• Constructor functions are similar to regular functions but are named with a capital letter to distinguish them from regular functions.
• To instantiate a new object, we use the new keyword followed by the constructor function and assign it to a variable with values defined as set during creation time.
• Constructor functions will never be used as regular functions by simply invoking them.

Default Parameters Values

• Default parameters are used to assign a default value to a parameter if no argument is passed to the function.
• Parameters defined earlier to default parameters can be available for default parameters.
• Default parameters can be used to avoid undefined values in code and provide alternate values if arguments are missing.
• The traditional way to solve this problem is to implement a series of checks in the function's body and provide alternate values if arguments are missing.

Learn about JavaScript functions, their importance, and how they prevent redundancy in code. Understand function declaration, syntax, and usage.