JavaScript Functions

Understanding Functions in JavaScript

Functions are reusable blocks of code that perform a specific task. They can take inputs, called parameters, and can return outputs. Functions help organize code and make it more modular.

Example 1: Basic Function

 function myFun() {
     console.log("hello")
     console.log("DeathCode")
 }
 
 myFun()

This is a simple function named myFun that logs two messages to the console. It is invoked by calling myFun().

Example 2: Function with Return Value

 function add5and6(){
     let sum = 5 + 6
     return sum
 }
 
 console.log(add5and6())

The add5and6 function calculates the sum of 5 and 6 and returns the result. The returned value is then logged to the console.

Example 3: Function with Parameters

 function addTwoNumbers(a, b){
     let sum = a + b;
     console.log(sum)
 }
 
 addTwoNumbers(5, 7);
 addTwoNumbers(6, 7);    

This function takes two parameters, a and b, calculates their sum, and logs it to the console. It is called multiple times with different arguments.

Example 4: Returning Values from Functions

 function addTwoNumbers(a, b){
     return a + b;
 }
 
 console.log(addTwoNumbers(14, 78));
 console.log(addTwoNumbers(45, 34));          

In this example, the function addTwoNumbers returns the sum of its parameters. The returned values are logged to the console.

Example 5: Function with Rest Parameters

 function addNumbers(...numbers){
     let sum = 0;
     for(let i = 0; i < numbers.length; i++){
        sum += numbers[i];
     }
     return sum;
}
 
 console.log(addNumbers(1, 2, 3, 298374, 238, 238947));

This function uses the rest parameter syntax (...numbers) to accept an arbitrary number of arguments. It calculates the sum of all provided numbers and returns the result.

Example 6: Modifying Objects

 function myFun3(o){
    o.email = "example@example.com"
 }
 
 let user = {
     name: "John",
     age: 30,
     email: "john@example.com",
 }
 console.log(user);
 myFun3({...user});
 console.log("After calling Function: ", user);

This example demonstrates how functions can modify objects. The function myFun3 attempts to change the email property of the user object. However, since a new object is created using the spread operator ({...user}), the original user object remains unchanged.

Conclusion

In this document, we explored the fundamentals of functions in JavaScript, including how to define, invoke, and return values from functions. We also examined the use of parameters and the spread operator to manipulate objects. Understanding functions is crucial for writing efficient and organized code in JavaScript.