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JavaScript for Python Programmers

User-Defined Functions and Libraries

Explore the structure and use of user-defined functions in both JavaScript and Python. Understand how to define functions, pass arguments, and work with return values. Discover how user-defined libraries or modules help organize code in both languages. Learn to handle user input in JavaScript and Python, gaining hands-on experience with modular programming concepts essential for transitioning between these languages.

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In Python, a user-defined function is a block of statements that does a specific task. Once defined, it can be used throughout the program. Functions are named and parameterized, with the def keyword preceding the function name and parameters. The function body contains the code that will be executed when the function is called.

Python 3.5
# Function in Python with a local variable
def greet(name):
  greeting = "Hello, " + name  # 'greeting' is a local variable
  return greeting
# Calling the function
message = greet("David")
print(message)

In JavaScript, functions are similar to those in Python. A function is defined using the function keyword, followed by the function name and parameters within parentheses. The function body contains the code that will be executed when the function is called.

Javascript (babel-node)
// Function in JavaScript with a local variable
function greet(name) {
  let greeting = "Hello, " + name;  // 'greeting' is a local variable
  return greeting;
}
// Calling the function
let message = greet("David");
console.log(message);

Note: In both examples, the function greet takes a string name as input and returns a greeting message. This demonstrates how a function can encapsulate a specific task, enhancing code reusability and readability.

Let’s understand the structure of a function with the help of an illustration:

Function name
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Function name

  • Function name: It is a unique identifier that represents the function and is used to call the function from ...