Functions and Prototypes in JavaScript

Functions

• Particular business logic is called a function
• Functions are used to reuse the business logic
• As per year ES6 to ES11 we’ve following type of functions :
  (a) Named function
  (b) Anonymous / arrow / callback function
  (c) Rest parameters in function
  (d) Optional parameters in function
  (e) Default parameters in function
  (f) Constructor functions

Named function

• The function with the name is called the named function

Anonymous function or Arrow function or callback function

• The function without a name is called an anonymous function
• It is also called Arrow function
• Arrow function concept introduced in ES6
• An arrow function is secured compared to the other functions
• Arrow functions behave like callback functions

Rest parameters in function

• “…” technically called as spread operator
• Spread operator introduced in ES6
• The spread operator has the capability to hold multiple values
• Because of spread operator argument behaves like an array
• The default value of spread operator augment is “[ ]”

NOTE: We can’t take more than one rest parameters.

Optional parameters in function

• While calling the functions few parameters are optional
• We’ll represent optional parameters by using “?”
• This concept also introduced in ES6
• Optional parameters will work in “Typescript environment”
• Superset of JavaScript is called as “Typescript”

Environmental setup of Typescript

• where “npm” stands for node packaging manager
• “npm” is the inbuilt tool for node.js
• “npm” helps to install Typescript
• “-g” stands for global installation

Execution of Typescript

• Typescript file should’ve the extension “.ts”
• We will execute Typescript by using “tsc” tool
• “tsc” stands for Typescript compiler
• If we execute Typescript in current path equalent “JavaScript” file will be generated
• Converting Typescript to equivalent JavaScript is called as transpilation

Default parameters in function

• While defining the functions, we initialize parameters with default values
• Default parameters also introduced in ES6

Constructor parameters in function

• It helps to create the classes like structure in JavaScript
• In the constructor function, all members (variables and functions) should start with “this” keyword

Parameterized constructor

Prototypes in JavaScript

• The prototype is the predefined property in JavaScript
• Prototype property helps to add the properties and functions to existed class dynamically

Prototype chaining (Inheritance)

• Getting the properties from the parent class to child class called as prototype chaining
• create() is the predefined function in object class helps to implement the prototype chaining in JavaScript

SINGLE INHERITANCE EXAMPLE

MULTIPLE INHERITANCE