Equality, Truthiness, and Falsy Values

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Lesson format7 sections1 code block1 practice itemUpdated Aug 23, 2026

#Most JavaScript bugs that look mysterious at first are ordinary value, conversion, or binding mistakes. The useful skill is learning exactly what value a variable holds at each step. In this lesson, the practical target is equality, truthiness, and falsy values: 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

console.log('0' == 0);
console.log('0' === 0);
console.log(Boolean('0'));
console.log(Boolean(''));

Live JavaScript preview

This example demonstrates equality, truthiness, and falsy values 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.

note

★ 20 XP

challenge BLOCK (★ 20 XP)

Which statement best matches the behavior taught in “Equality, Truthiness, and Falsy Values”?

Select your proof vectors above

The common trap is to memorize syntax while missing the boundary around it. Watch the inputs, the resulting value, and the point where the browser or Node.js host takes over.

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

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Most JavaScript bugs that look mysterious at first are ordinary value, conversion, or binding mistakes. The useful skill is learning exactly what value a variable holds at each step. In this lesson, the practical target is equality, truthiness, and falsy values: 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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curl -H "Accept: text/markdown" "https://vulnarex.com/api/content/lessons?courseSlug=complete-javascript-course&lessonSlug=equality-truthiness-and-falsy-values&lang=en&format=markdown"

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

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?