[TOC] ## 概述 `Person`沒有明確說明是基于`Named`的,但是有也不錯報錯 ``` interface Named { name: string; } class Person { name: string; } let p: Named; // OK, because of structural typing p = new Person(); ``` ## 符合接口的賦值 只要變量符合接口的屬性即可,額外屬性不會報錯 ``` interface Named { name: string; } let x: Named; // y's inferred type is { name: string; location: string; } let y = { name: 'Alice', location: 'Seattle' }; x = y; ``` ## 比較兩個函數 額外參數在 js 中非常常見 ``` let x = (a: number) => 0; let y = (b: number, s: string) => 0; y = x; // OK x = y; // Error ``` 返回值比較 ``` let x = () => ({name: 'Alice'}); let y = () => ({name: 'Alice', location: 'Seattle'}); x = y; // OK y = x; // Error, because x() lacks a location property ``` ## 函數重載 ### 枚舉 枚舉類型與數字類型兼容，并且數字類型與枚舉類型兼容。不同枚舉類型之間是不兼容的 ``` enum Status { Ready, Waiting }; enum Color { Red, Blue, Green }; let status = Status.Ready; status = Color.Green; // Error ```