60 lines
1.5 KiB
Plaintext
60 lines
1.5 KiB
Plaintext
// @flow strict
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import { SYMBOL_ITERATOR } from '../polyfills/symbols';
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/**
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* Safer version of `Array.from` that return `null` if value isn't convertible to array.
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* Also protects against Array-like objects without items.
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*
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* @example
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*
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* safeArrayFrom([ 1, 2, 3 ]) // [1, 2, 3]
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* safeArrayFrom('ABC') // null
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* safeArrayFrom({ length: 1 }) // null
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* safeArrayFrom({ length: 1, 0: 'Alpha' }) // ['Alpha']
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* safeArrayFrom({ key: 'value' }) // null
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* safeArrayFrom(new Map()) // []
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*
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*/
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export default function safeArrayFrom<T>(
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collection: mixed,
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mapFn: (elem: mixed, index: number) => T = (item) => ((item: any): T),
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): Array<T> | null {
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if (collection == null || typeof collection !== 'object') {
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return null;
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}
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if (Array.isArray(collection)) {
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return collection.map(mapFn);
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}
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// Is Iterable?
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const iteratorMethod = collection[SYMBOL_ITERATOR];
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if (typeof iteratorMethod === 'function') {
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// $FlowFixMe[incompatible-use]
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const iterator = iteratorMethod.call(collection);
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const result = [];
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let step;
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for (let i = 0; !(step = iterator.next()).done; ++i) {
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result.push(mapFn(step.value, i));
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}
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return result;
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}
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// Is Array like?
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const length = collection.length;
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if (typeof length === 'number' && length >= 0 && length % 1 === 0) {
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const result = [];
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for (let i = 0; i < length; ++i) {
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if (!Object.prototype.hasOwnProperty.call(collection, i)) {
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return null;
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}
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result.push(mapFn(collection[String(i)], i));
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}
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return result;
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}
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return null;
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}
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