Set and Map

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Lesson format7 sections1 code block1 practice itemUpdated Aug 23, 2026

#The deeper object model explains why two variables can appear independent while changing the same value underneath. These lessons focus on references, built-in collections, and structured data. In this lesson, the practical target is set and map: you should be able to predict what the runtime will do before changing the code.#link

Observation	Diagnostic question
Runtime value	What value actually arrived?
Language rule	Which rule determines the result?

javascript

const seen = new Set(['a', 'b', 'a']);
const scores = new Map([['mina', 92]]);
console.log(seen.size, scores.get('mina'));

Live JavaScript preview

This example demonstrates set and map directly. Change one input at a time and observe the result; the goal is to connect the syntax to the runtime behavior rather than treating the snippet as a recipe.

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quiz BLOCK (★ 20 XP)

Which statement best matches the behavior taught in “Set and Map”?

Select your proof vectors above

A common failure with set and map is changing several variables at once. That hides which rule actually caused the result.

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The deeper object model explains why two variables can appear independent while changing the same value underneath. These lessons focus on references, built-in collections, and structured data. In this lesson, the practical target is set and map: you should be able to predict what the runtime will do before changing the code.

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August 23, 2026

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Laboratory sanity code

Isolate active probes on matched virtual networks and keep execution streams sandboxed.

Observation

Diagnostic question

Runtime value

What value actually arrived?

Language rule

Which rule determines the result?