Copying instead of mutating in JavaScript

The 2023 methods return a new array where the old ones edited in place.

const original = [3, 1, 2];

const sorted = original.toSorted((a, b) => a - b);
const reversed = original.toReversed();
const replaced = original.with(0, 99);
const spliced = original.toSpliced(1, 1);

console.log(original, sorted, reversed, replaced, spliced);

const mutated = [3, 1, 2];
mutated.sort();
console.log(mutated); // the original order is gone

console.log([[1, [2]], [3]].flat(2), Array.from({ length: 3 }, (_, i) => i));

How it works

1. toSorted, toReversed and with leave the original alone.
2. sort and reverse still mutate, which surprises people.
3. at, flat and spread cover the rest.

Keywords and builtins used here

• Array
• const
• from
• with

The run, in numbers

Lines

14

Characters to type

436

Tokens

145

Three-star pace

90 tpm

At the three-star pace of 90 tokens a minute, this run takes about 97 seconds.

Type this snippet

Step 3 of 10 in Arrays, step 19 of 43 in Language basics.

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