map, filter, and reduce

A structured lesson workspace with readable content, hands-on examples, and a clean path to completion.

Lesson format7 sections1 code block1 practice itemUpdated Aug 23, 2026

#This example demonstrates map, filter, and reduce 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.#link

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

javascript

const amounts = [10, 20, 30];
const doubled = amounts.map(n => n * 2);
const large = amounts.filter(n => n >= 20);
const total = amounts.reduce((sum, n) => sum + n, 0);
console.log(doubled, large, total);

Live JavaScript preview

Keep the experiment focused on map, filter, and reduce and change one assumption at a time.

★ 20 XP

SYNTAX VALIDATION (★ 20 XP)

Which statement best matches the behavior taught in “map, filter, and reduce”?

root@vulnarex:~#

Press Enter to submit

This example demonstrates map, filter, and reduce 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.

Lesson completion

Ready to resolve this lesson?

Finish the lesson once you have worked through the material. This awards ★ 20 XP.

Previous lesson

Lesson tools

Workspace

0% read

Lab notes

Notes persist per lesson.

Content

Last updated

August 23, 2026

Agent Setup

Access lesson content programmatically for AI agents, LLMs, and automated pipelines.

Fetch as Markdown (Accept header)

curl -H "Accept: text/markdown" "https://vulnarex.com/api/content/lessons?courseSlug=complete-javascript-course&lessonSlug=map-filter-and-reduce&lang=en&format=markdown"

MCP Server Config (mcp.json)

{
  "mcpServers": {
    "vulnarex": {
      "command": "npx",
      "args": ["-y", "@modelcontextprotocol/server-fetch"],
      "env": { "MCP_FETCH_URL": "https://vulnarex.com" }
    }
  }
}

MCP Server Card/.well-known/mcp.json A2A Agent Card/.well-known/agent-card.json API Catalog/.well-known/api-catalog robots.txt/robots.txt

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?

const amounts = [10, 20, 30];

const doubled = amounts.map(n => n * 2);

const large = amounts.filter(n => n >= 20);

const total = amounts.reduce((sum, n) => sum + n, 0);

console.log(doubled, large, total);