Functions

A function is a named block of code that does one job. You write it once and use it as many times as you like.

Why Use Functions?

You have already used functions: print() in Python and console.log() in JavaScript. Someone else wrote them, and you just call them by name.

Writing your own functions helps you:

• Avoid repeating code: write the steps once, use them everywhere
• Keep code organised: each function has one clear job
• Fix bugs in one place: change the function and every use is fixed

Defining and Calling a Function

Python uses the word def; JavaScript uses the word function.

def greet():
    print("Welcome to Workownix!")
    print("Let's start learning.")

greet()
greet()

Welcome to Workownix!
Let's start learning.
Welcome to Workownix!
Let's start learning.

function greet() {
  console.log("Welcome to Workownix!");
  console.log("Let's start learning.");
}

greet();
greet();

Welcome to Workownix!
Let's start learning.
Welcome to Workownix!
Let's start learning.

Defining a function does not run it. The code inside runs only when you call it by writing its name followed by brackets (). We called it twice, so the message appears twice.

Parameters: Giving a Function Input

A function becomes more useful when you can give it information. The names inside the brackets are called parameters. The values you pass in when calling are called arguments.

def greet(name):
    print("Hello,", name)

greet("Ali")
greet("Ayesha")

Hello, Ali
Hello, Ayesha

function greet(name) {
  console.log("Hello,", name);
}

greet("Ali");
greet("Ayesha");

Hello, Ali
Hello, Ayesha

A function can take more than one parameter. Separate them with commas, for example def bill(price, quantity):.

Returning a Value

Often you want a function to work something out and give back the answer, so you can store or use it. For that we use return.

def bill(price, quantity):
    return price * quantity

total = bill(150, 4)
print("Total: Rs", total)
print("Two pizzas: Rs", bill(1200, 2))

Total: Rs 600
Two pizzas: Rs 2400

function bill(price, quantity) {
  return price * quantity;
}

let total = bill(150, 4);
console.log("Total: Rs", total);
console.log("Two pizzas: Rs", bill(1200, 2));

Total: Rs 600
Two pizzas: Rs 2400

When the computer reaches return, the function stops and the value goes back to the place where it was called.

Putting It All Together

Functions can use conditions and loops inside them. This one decides whether a student has passed:

def result(marks):
    if marks >= 50:
        return "Pass"
    return "Fail"

for m in [78, 45, 50]:
    print(m, result(m))

78 Pass
45 Fail
50 Pass

function result(marks) {
  if (marks >= 50) {
    return "Pass";
  }
  return "Fail";
}

for (let m of [78, 45, 50]) {
  console.log(m, result(m));
}

78 Pass
45 Fail
50 Pass

Quick Comparison

Exercise