update docs

src/docs/blog/4.md

@@ -54,6 +54,95 @@ const arr2 = [4, 5, 6]
 console.log(myConcat(0, arr1, arr2)) // [0, 1, 2, 3, 4, 5, 6]
 ```
 
+## Array.prototype.copyWithin()
+
+```js
+function copyWithin(arr, target, start, end) {
+  const len = arr.length
+  const copy = []
+  const copyLen = end - start
+
+  target = Math.floor(target)
+  start = Math.floor(start)
+  end = Math.floor(end)
+
+  if (target >= len || start >= len || end < start) {
+    return arr
+  }
+
+  if (target < -len) {
+    target = 0
+  }
+  else if (target < 0) {
+    target = target + len
+  }
+
+  if (start < -len) {
+    start = 0
+  }
+  else if (start < 0) {
+    start = start + len
+  }
+
+  if (end < -len) {
+    end = 0
+  }
+  else if (end < 0) {
+    end = end + len
+  }
+  else if (end > len) {
+    end = len
+  }
+
+  for (let i = start; i < end; i++) {
+    copy[copy.length] = arr[i]
+  }
+
+  for (let i = 0; i < copyLen; i++) {
+    arr[target++] = copy[i]
+    if (target === len) {
+      break
+    }
+  }
+
+  return arr
+}
+
+const arr = ['a', 'b', 'c', 'd', 'e']
+console.log(copyWithin(arr, 3, 2, 5)) // ['a', 'b', 'c', 'c', 'd']
+```
+
+## Array.prototype.entries()
+
+```js
+function myEntries(arr) {
+  const len = arr.length
+  const entries = []
+
+  for (let i = 0; i < len; i++) {
+    entries.push(arr[i])
+  }
+
+  entries[Symbol.iterator] = () => {
+    let index = 0
+    return {
+      next: () =>
+        index < values.length
+          ? { value: [index, entries[index++]], done: false }
+          : { value: undefined, done: true },
+    }
+  }
+
+  return entries
+}
+
+// test
+const arr = [1, 2, 3]
+for (const [k, v] of myEntries(arr)) {
+  console.log(k, v) // 0 1 \n 1 2 \n 2 3
+}
+```
+
 ## Array.prototype.every()
 
 ```js