Adding, Removing, and Updating Array Elements

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Lesson format7 sections1 code block1 practice itemUpdated Aug 23, 2026

#Arrays and objects are the everyday containers of JavaScript applications. Knowing their mutation rules and iteration behavior is more valuable than memorizing a long method list. In this lesson, the practical target is adding, removing, and updating array elements: 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 queue = ['build', 'test'];
queue.push('deploy');
console.log(queue[0], queue.length);

Live JavaScript preview

Keep the experiment focused on adding, removing, and updating array elements and change one assumption at a time.

★ 20 XP

exercise BLOCK (★ 20 XP)

Type one representative JavaScript construct used to demonstrate adding, removing, and updating array elements.

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note

Production code makes this matter quickly: a small assumption about adding, removing, and updating array elements can surface as a UI bug, a failed request, a test that flakes, or a process that exits earlier than expected.

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

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Arrays and objects are the everyday containers of JavaScript applications. Knowing their mutation rules and iteration behavior is more valuable than memorizing a long method list. In this lesson, the practical target is adding, removing, and updating array elements: 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?