Merge branch 'writing'

docs/article/2019/js-copy.md

@@ -216,22 +216,33 @@ console.log(arr, arr4);
 
 递归方法实现深度克隆原理：遍历对象、数组直到里边都是基本数据类型，然后再去复制，就是深度拷贝
 
-```js
-function deepCopy(target, origin) {
-  target = target || {};
-  let toStr = Object.prototype.toString,
-    arrStr = "[object Array]";
-  for (let prop in origin) {
-    if (origin[prop] !== "null" && typeof origin[prop] == "object") {
-      toStr.call(origin[prop]) == arrStr
-        ? (target[prop] = [])
-        : (target[prop] = {});
-      deepCopy(target[prop], origin[prop]);
-    } else {
-      target[prop] = origin[prop];
+```ts
+function deepCopy(from: any, map: any = new Map()) {
+  const isObject = (obj: any): obj is Object =>
+    Object.prototype.toString.call(obj) === "[object Object]" ||
+    Object.prototype.toString.call(obj) === "[object Array]";
+
+  if (!isObject(from)) return from;
+  let res: any = Array.isArray(from) ? [] : {};
+
+  // 有缓存时不用递归，解决循环引用问题
+  if (map.get(from)) res = map.get(from);
+  else {
+    // 缓存当前对象
+    map.set(from, res);
+    for (const key of [
+      ...Object.keys(from),
+      ...Object.getOwnPropertySymbols(from),
+    ]) {
+      const val = from[key];
+      if (isObject(val)) {
+        res[key] = deepCopy(val, map);
+      } else {
+        res[key] = val;
+      }
     }
   }
-  return target;
+  return res;
 }
 ```
 
@@ -243,7 +254,7 @@ let a = {
   say: function() {},
   m: Symbol(1)
 };
-const b = deepCopy({}, a)
+const b = deepCopy(a)
 b.age = 12
 b.arr[1] = 4
 b.m = Symbol(2)