Remove Duplicates

Console

BeginnerArrays

Task

Implement `removeDuplicates(items)` that returns a new array keeping only the **first occurrence** of each value, preserving order. The one-liner uses a Set: `[...new Set(items)]`. Also worth writing the manual filter/indexOf version to understand what Set buys you.

Hints

0 / 2

A Set automatically ignores repeated values.
To preserve first-seen order manually: items.filter((x, i) => items.indexOf(x) === i).

Verification tests

removeDuplicates([1,2,2,3,1])→ [1,2,3]
removeDuplicates(["a","b","a","c"])→ ["a","b","c"]
removeDuplicates([])→ []
removeDuplicates([5,5,5])→ [5]

⚠️ Reveal official solutions

Try solving it yourself first — struggling is where the learning happens.

Recommended — the idiomatic Set one-liner.

function removeDuplicates(items) {
  return [...new Set(items)];
}

Use when asked to avoid Set, or to show the underlying logic.

function removeDuplicates(items) {
  const out = [];
  for (const x of items) {
    if (!out.includes(x)) out.push(x);
  }
  return out;
}

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