Count Items Matching a Rule LeetCode solution in JavaScript

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const RULE_IDX = {
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  type: 0,
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  color: 1,
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  name: 2,
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};
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var countMatches = function (items, ruleKey, ruleValue) {
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  return items.reduce(
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    (ans, item) => (item[RULE_IDX[ruleKey]] === ruleValue ? ans + 1 : ans),
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    0
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  );
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};