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Intermediate 20 min readModule: Module 5: Objects, Arrays & Modern ES6+ Methods

Array Methods (map/filter/reduce), Maps & Sets

Transform collections with map, filter, and reduce, and leverage high-performance Map and Set collections.

What You Will Learn in This Lesson

  • Data transformation pipelines with .map(), .filter(), and .reduce()
  • Unique collections with Set for O(1) deduplication
  • Key-value indexing with Map supporting non-string keys

Introduction & Core Concept

Modern JavaScript provides high-performance data structures: Arrays for ordered sequences, Sets for unique values, and Maps for arbitrary key-value mappings.
WHY DOES THIS MATTER IN THE REAL WORLD?

Deduplicating an array with new Set(arr) runs in O(n) time compared to O(n²) nested loop searches.

Array Transformation & Set Deduplication

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const rawTags = ["react", "nextjs", "react", "typescript", "nextjs"];
const uniqueTags = [...new Set(rawTags)];
console.log("Unique Tags:", uniqueTags);
 
const scores = [85, 92, 78, 96];
const avg = scores.reduce((acc, s) => acc + s, 0) / scores.length;
console.log("Average Score:", avg);

Line-by-Line Technical Breakdown

1Map and Set provide O(1) average time complexity for insertions and lookups.

Try It Yourself (Interactive Editor)

Modify the code in real-time and click Run to test live browser output and console logs.

Intelligent Code Runner & Live Sandbox[JAVASCRIPT]
JAVASCRIPT SOURCE EDITOR
Interactive Live Code

Industry Best Practices & Professional Standards

  • Use Map over plain objects when keys are dynamic or non-string types.

Lesson Summary & Core Takeaways

  • Collections and functional methods enable concise, expressive data transformations.