Array Iteration Methods

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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 array iteration methods: 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

This example demonstrates array iteration methods 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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exercise BLOCK (★ 20 XP)

Which statement best matches the behavior taught in “Array Iteration Methods”?

Select your proof vectors above

callout

A common failure with array iteration methods is changing several variables at once. That hides which rule actually caused the result.

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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 array iteration methods: 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?