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