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23 lines
482 B
23 lines
482 B
2 years ago
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'use strict';
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/**
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* If `map` already has the given `key`, returns its value. Otherwise, calls
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* `callback`, adds the result to `map` at `key`, and then returns it.
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*
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* @template K
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* @template V
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* @param {Map<K, V>} map
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* @param {K} key
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* @param {() => V} callback
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* @returns {V}
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*/
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module.exports = function putIfAbsent(map, key, callback) {
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if (map.has(key)) return /** @type {V} */ (map.get(key));
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const value = callback();
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map.set(key, value);
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return value;
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};
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