fix(flatten): use for loop to avoid stack issues (#116)

* test(flatten): reproduce #108

* fix(flatten): use for loop to avoid stack issues

Author: mmkal

src/flatten.ts

@@ -1,6 +1,7 @@
-export const flattenDeep = (args: any[]): any[]  => {
-    if (!Array.isArray(args)) {
-        return args;
+export const flattenDeep = (array: any[]): any[]  => {
+    const flat = [] as any[];
+    for (const item of array) {
+        Array.isArray(item) ? flat.push(...flattenDeep(item)) : flat.push(item);
     }
-    return [].concat(...args.map(flattenDeep) as any);
+    return flat;
 };

test/flatten.test.ts

@@ -1,4 +1,5 @@
 import { flattenDeep } from "../src/flatten";
+import {range} from "lodash";
 
 it("is already flat", () => {
     expect(flattenDeep([1, 2, 3])).toEqual([1, 2, 3]);
@@ -11,3 +12,8 @@ it("flattens shallowly", () => {
 it("flattens deeply", () => {
     expect(flattenDeep([1, 2, [3, [4, [5]]]])).toEqual([1, 2, 3, 4, 5]);
 });
+
+it("flattens huge arrays", () => {
+    const huge = range(0, 500000);
+    expect(flattenDeep(huge)).toEqual(huge);
+});