Add ts interfaces

src/SUMMARY.md

@@ -16,6 +16,8 @@
     - [Testing](./dev/rust/testing.md)
   - [Ruby](./dev/ruby/main.md)
     - [arrays](./dev/ruby/arrays.md)
+  - [TypeScript](./dev/ts/main.md)
+    - [interfaces](./dev/ts/interfaces.md)
   - [Web](./dev/web/main.md)
     - [front](./dev/web/front/main.md)
       - [babel and babel-preset-stage-2](./dev/web/front/babel-preset-stage-2.md)

src/dev/ts/interfaces.md

@@ -0,0 +1,61 @@
+# Interfaces in TypeScript
+
+[Handbook](https://www.typescriptlang.org/docs/handbook/interfaces.html)
+
+## Overview
+
+Interface in TypeScripts are used to create a _blueprint_ or an abstraction of a class.
+
+An interface can contains properties (_mandatory_, _optional_ or _readonly_)
+
+```typescript
+interface Example {
+  mandatory: string;
+  optional?: string;
+  readonly ro: string;
+}
+```
+
+And methods
+
+```typescript
+interface Example {
+  mandatory: string;
+  optional?: string;
+
+  concat(sep: string): string;
+}
+```
+
+To use the interface, a class should **implement** it,
+
+```typescript
+class Impl implements Example {
+  mandatory: string;
+  optional?: string;
+
+  constructor(m: string, o: string) {
+    this.mandatory = m;
+    this.optional = o;
+  }
+
+  contact(sep: string): string {
+    return `${this.mandatory}${sep}${this.optional}`;
+  }
+}
+```
+
+## The Promise case
+
+What about a promise based method ? Do not forget what async/await does. It wraps all the things in `Promise<T>`.
+
+In order to add promise to your interface, just specify a Promise as return type.
+
+```typescript
+interface Example {
+  mandatory: string;
+  optional?: string;
+
+  promize(arg: string): Promise<string>;
+}
+```