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Arrays · medium

23. Arrays: Transformations & Non-Mutating Methods

Transformations and modern copying array operations.

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Standard methods like `sort()` and `splice()` mutate the source array in place. Modern JavaScript provides non-mutating counterparts: `toSorted()`, `toReversed()`, `toSpliced()`, and `with()` which return fresh copies.

js
const blocks = [300, 100, 200];
const sorted = blocks.toSorted((a, b) => a - b); // [100, 200, 300], blocks unchanged
const updated = blocks.with(0, 400);              // [400, 100, 200]

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  1. 1. What is the key difference between sort() and toSorted()?

  2. 2. Which method replaces an element at an index without mutating the source array?

  3. 3. Why pass an initial value to reduce()?

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