feat: add flat function

Author: chachaxw

js/flat.js

@@ -0,0 +1,46 @@
+/**
+ *
+ * @param {*} array 深层嵌套的数据
+ * @returns array 新数组
+ */
+const flat1 = (array) => {
+    return array.reduce((result, it) => {
+        return result.concat(Array.isArray(it) ? flat1(it) : it);
+    }, []);
+};
+
+let arr1 = [1, [2, 3, 4], [5, [6, [7, [8]]]]];
+console.log(flat1(arr1));
+
+// js原生的flat方法
+/**
+ *
+ * @param {*} array 深层嵌套的数据
+ * @returns 新数组
+ */
+const flat2 = (array) => {
+    return array.flat(Infinity);
+};
+
+let arr2 = [1, [2, 3, 4], [5, [6, [7, [8]]]]];
+
+console.log(flat2(arr2));
+
+const flat3 = (array) => {
+    const result = [];
+    const stack = [...array];
+
+    while (stack.length !== 0) {
+        const val = stack.pop();
+        if (Array.isArray(val)) {
+            stack.push(...val);
+        } else {
+            result.unshift(val);
+        }
+    }
+    return result;
+};
+
+let arr3 = [1, [2, 3, 4], [5, [6, [7, [8]]]]];
+
+console.log(flat3(arr3));