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devexamples

Deduplicate Arrays by Key Keeping First Item

Remove duplicate objects from an array using a key function or property name, preserving original order and first occurrences.

JavascriptData Integrity

Code

snippet
export function uniqueBy(items, keyFn) {
  if (!Array.isArray(items)) throw new TypeError("items must be an array");
  if (typeof keyFn !== "function") throw new TypeError("keyFn must be a function");
  const seen = new Set();
  const result = [];
  for (const item of items) {
    const key = keyFn(item);
    if (seen.has(key)) continue;
    seen.add(key);
    result.push(item);
  }
  return result;
}

export function uniqueByProperty(items, property) {
  if (typeof property !== "string" || property.length === 0) {
    throw new TypeError("property must be a non-empty string");
  }
  return uniqueBy(items, (item) => {
    if (item === null || typeof item !== "object") {
      throw new TypeError("items must contain objects");
    }
    return item[property];
  });
}

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