Pure functions Vs. Impure functions

In JavaScript, functions can be categorized as either pure functions or impure functions based on their behavior and effects. These categories help us understand how functions interact with data, maintain predictability, and manage side effects. Let's investigate into the details of both types, along with examples:

Pure Functions

A pure function is a function that, given the same input, always produces the same output and has no side effects. In other words, its behavior is solely determined by its input parameters, and it doesn't modify any external state or data.

Characteristics of pure functions

  1. Deterministic: The same input will always result in the same output.
  2. No side effects: They don't modify external data or have observable interactions with the outside world, such as changing global variables, making network requests, or modifying the DOM.

Benefits of pure functions

  1. Predictable behavior
  2. Easier to test and reason about
  3. Can be parallelized and memoized
Example of a pure function:
function add(a, b) { return a + b; }

Impure Functions

An impure function is a function that has side effects or produces different output for the same input. Side effects can include modifying external data, printing to the console, making network requests, etc.

Characteristics of impure functions

  1. Side effects: They have actions beyond returning a value, like modifying external state.
  2. Non-deterministic: They can produce different results for the same input due to external factors.
Examples of impure functions:
let total = 0; // External state function addToTotal(amount) { total += amount; // Modifies external state } function getRandomNumber() { return Math.random(); // Non-deterministic result } function logMessage(message) { console.log(message); // Console output }
Examples of Impure Functions with Side Effects:
// Modifying global variable let counter = 0; function incrementCounter() { counter++; } // Making network request function fetchDataFromServer() { // Simulated network request return fetch('https://api.example.com/data'); } // Using and modifying external state const itemList = []; function addItemToList(item) { itemList.push(item); console.log(`Added ${item} to the list`); }

Understanding the distinction between pure and impure functions is crucial when designing robust and maintainable code.

Conclusion

Pure functions are generally favored as they lead to more predictable and testable codebases. Impure functions can introduce complexity and make it harder to reason about the behavior of the code. However, both types of functions have their place in programming; impure functions are necessary for interacting with the external world and producing side effects. The key is to manage impurity carefully and isolate it when necessary to maintain code clarity and predictability.






Related Topics
  1. JavaScript Interview Questions (Part2)
  2. JavaScript Interview Questions (Part3)
  3. Is JavaScript a true OOP language?
  4. Advantages and Disadvantages of JavaScript
  1. Difference Between JavaScript and ECMAScript?
  2. What is noscript tag?
  3. Escaping Special Characters in JavaScript
  4. What is undefined x 1 in JavaScript?
  5. Logical operators in JavaScript
  6. Difference between '=', '==' and '===' operators in JS
  7. How to loop through objects in JavaScript?
  8. How to write html code dynamically using JavaScript?
  9. How to add html elements dynamically with JavaScript?
  10. How to load another html page from javascript?
  11. What Is The Disadvantages Using InnerHTML In JavaScript?
  12. What is Browser Object Model
  13. How to detect the OS on the client machine in JavaScript?
  14. Difference between window, document, and screen in Javascript?
  15. Difference between the substr() and substring() in JavaScript?
  16. How to replace all occurrences of a string in JavaScript?
  17. Test a string as a literal and as an object in JavaScript
  18. What is Associative Array in JavaScript
  19. What is an anonymous function in JavaScript?
  20. What is the use of 'bind' method in JavaScript?
  21. Is Javascript a Functional Programming Language?
  22. What's the Difference Between Class and Prototypal Inheritance?
  23. Javascript, Pass by Value or Pass by Reference?
  24. How to prevent modification of an object in Javascript?
  25. What is 'this' keyword in JavaScript?
  26. How Does Function Hoisting Work in JavaScript?
  27. What do mean by NULL in Javascript?
  28. What does the delete operator do in JavaScript?
  29. What is the Infinity property used for in Javascript?
  30. Event bubbling and Event Capturing in JavScript?
  31. What is "strict mode" and how is it used in JavaScript?
  32. What is the difference between call and apply in JavaScript
  33. Entire content of a JavaScript source file in a function block?
  34. What is an immediately-invoked function expression?
  35. What is escape & unescape String functions in JavaScript?
  36. Instanceof operator in JavaScript
  37. What Are RESTful (REpresentational State Transfer)Web Services?
  38. What is Unobtrusive JavaScript & Why it's Important?
  39. What Does JavaScript Void(0) Mean?
  40. What are JavaScript Cookies?
  41. Difference between Client side JavaScript and Server side JavaScript
  42. TypeError: document.getelementbyid(...) is null
  43. Uncaught TypeError: Cannot read property of undefined In JavaScript
  44. Null and Undefined in JavaScript