feat: type assertion

Author: Rain120

CHANGELOG.md

@@ -1,11 +1,12 @@
-# 1.0.0 (2020-07-15)
+# 1.0.0 (2020-07-27)
 
 
 ### Bug Fixes
 
 * monaco editor build bug (cannot require async component) ([906f6e8](https://github.com/Rain120/typescript-guide/commit/906f6e8379efe762d76f16381b657e4752be4dd4))
 * monaco editor show normal modal and can edit ([da7a4c9](https://github.com/Rain120/typescript-guide/commit/da7a4c9316b6bf245ceccea93f3518ddaf810f80))
 * nested sub-level directories path ([c6830ac](https://github.com/Rain120/typescript-guide/commit/c6830ac37ada02270874d8d3d7ab00fade02e51d))
+* README OKR path not found ([5d9739d](https://github.com/Rain120/typescript-guide/commit/5d9739d17602787fb8d1ad190d225fc572003920))
 * update google analysis id ([2e1721b](https://github.com/Rain120/typescript-guide/commit/2e1721b7f5a7b671398f5d6ec2c094194c4229c0))
 
 

README.md

@@ -39,7 +39,7 @@ Learning all about the base of Typescript, and practice it
 
 - [x] [Basic](./docs/zh/basic/README.md)
 
-- [ ] [Type Assertion](./docs/zh/type-assertion/README.md)
+- [x] [Type Assertion](./docs/zh/type-assertion/README.md)
 
 - [ ] [Union Types](./docs/zh/union-types/README.md)
 

docs/zh/guide/README.md

@@ -40,7 +40,7 @@ Learning all about the base of Typescript, and practice it
 
 - [x] [Basic](../basic/README.md)
 
-- [ ] [Type Assertion](../type-assertion/README.md)
+- [x] [Type Assertion](../type-assertion/README.md)
 
 - [ ] [Union Types](../union-types/README.md)
 

docs/zh/type-assertion/README.md

@@ -1,15 +1,88 @@
 ## 定义
 
+有时候你会比 `Typescript` 更了解你的值的类型, `Typescript` 允许你使用你想要的方式分析并覆盖它, 这种机制被称为 **「类型断言」**。
+
 ## 使用
 
+类型断言有 **两种形式**:
+
+### as
+
+```ts
+const someValue: any = "this is a string";
+
+const strLength: number = (someValue as string).length;
+```
+
+### <> 尖括号
+
+```ts
+const someValue: any = "this is a string";
+
+const strLength: number = (<string>someValue).length;
+```
+
+**Note:** 当你在 **`.jsx`** `or` **`.tsx`** 中使用 **尖括号** 的方式进行类型断言时, 会造成 **语言歧义**, 为了保持一致性, 推荐使用 `as` 语法来进行 **类型断言**。[相关体验](https://www.typescriptlang.org/play?#code/JYOwLgpgTgZghgYwgAgApQPY2AGxQbwCgBIEOAWwgC5kBnMKUAcwG4S4nrkQBXcgI2jIAPnQbM2AX0KEEGEPWRweYABYYoyALzIAPOiy4IAPnyS2hZWo0A6MpW3IA5ACU4oAIwAmAAxPCQA)
+
+## 双重断言
+
+原理: 任何类型都可以被断言为 `any`, 而 `any` 可以被断言为任何类型。
+
+```ts
+interface Person {
+	name: string;
+}
+
+const mine = 'Rain120';
+
+((age as any) as Person).name;
+
+```
+
+**Note:** 双重断言极具破坏性, 而且它很可能会导致运行时错误, 慎用 !!!
+
+## 类型断言 与 类型转换
+
+在计算机科学中, **[类型转换 (type conversion)](https://zh.wikipedia.org/zh-cn/%E7%B1%BB%E5%9E%8B%E8%BD%AC%E6%8D%A2)** 是指将数据从一种类型 **转换成** 另一种类型的过程。所以 **类型转换** 是在 **运行时** 转换的, 而 **类型断言** 只是一个编译时的语法, 为编译器提供关于如何分析代码的方法。
+
+若要进行类型转换, 需要直接调用类型转换的方法:
+```ts
+Boolean();
+
+String();
+
+parseInt();
+
+// etc...
+```
+
+## 断言判断
+
+- **C类型** 是 **P类型** 的 **子类型**
+
+- **P类型** 是 **C类型** 的 **子类型**
+
+**C类型** 能被断言为 **P类型**。
+
 ## 快来耍耍啊
 
 ### 🌰🌰
 
 <!-- 题目 -->
 
-```
-// template
+请解决👇👇👇报错
+
+```ts
+interface Profile {
+	name: string;
+	age: number | string;
+}
+
+const author = {};
+
+// Property 'name' does not exist on type '{}'.(2339)
+author.name = 'Rain120';
+
 ```
 
 ### 游乐场
@@ -23,8 +96,24 @@
 ### 参考答案
 
 ```ts
-// answer
+
+interface Profile {
+	name: string;
+	age: number | string;
+}
+
+const author = {} as Profile;
+
+// const author = <Profile>{};
+
+author.name = 'Rain120';
+
 ```
 
 ## 参考资料
 
+[Handbook - type-assertion](https://www.typescriptlang.org/docs/handbook/basic-types.html#type-assertions)
+
+[深入理解 Typescript](https://jkchao.github.io/typescript-book-chinese/typings/typeAssertion.html)
+
+[Typescript - type-assertion](https://ts.xcatliu.com/basics/type-assertion.html)