flow like the river

VISUALIZACION/node_modules/graphql/jsutils/safeArrayFrom.js.flow

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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;
+}