Functions

• At their simplest form, functions are reusable blocks of code
  • These blocks of code are essential in DRY code

Functions in Depth

• functions take input (through arguments) and then produce an output

Syntax

function test () {
...
return ...
}

• First, we have to define our function and then name it
• In the parathesis () are our parameters
  • these parameters act as placeholders for our input
• inside the curly brackets we write our actual code that out function will do
• the return keyword would simply return any values produced from the function

• Calling the function
  • now that we defined our function, we need to use it in our code, we do that by calling the function

    test(...)
    

    • inside the parenthesis () is our arguments, which are the inputs that we want to work with

      Example

      here is an example of a function that adds 2 numbers

      // defining our function 
      function add(x, y){
      answer = x + y; 
      return answer; 
      }
      // calling our function 
      add (3, 5);
      

Expression vs Declaration functions

• Declaration of functions are used to create named functions
  • Example

    function add(x, y){
        return x + y
    

Function Expressions

• Function expressions are function that are stored inside variables
• These function are anonymous (without a name property)
• Syntax

      sum = function(x, y){
      return x - y 
        }
  

Arrow Functions (ES6+)

• By using the arrow notation => we don't require the function keyword to define the function

const sum = (x, y) => {   
return x + y;  
}

console.log(sum(2,5));

Variations of the Arrow Functions

• If we have only 1 parameter to our function, we don't need our parenthesis

    const log = x => {
    console.log (x)
    }
  

• If we have 1 expression in our function, we can do not need the return keyword

  const calcAge = age =>  2022 - birthyear
  

Function Calling other Functions

• Lets create a function that would first of all square the 2 arguments provided, then add them

  • First we need to define the first function that would square the 2 arguments

          function square(x) {
          const y = x ** 2;
          return y;
          }
    

  • Second we would call the function inside the function that would add the 2 squares

    function square(x) {
    const y = x ** 2;
    return y;
    }
    
    function sumOfSquares(x, y) {
    const a = square(x);
    const b = square(y);
    return a + b;
    }
    

• Finally we log the value of the function inside the console

    console.log(sumOfSquares(2, 3));