How to start typescript?

1. yarn init

2. yarn add typescript

3. yarn tsc --init // create tsconfig.json

4. if you don't exist "compilerOptions", "include", "exclude" in tsconfig.json, you add below code

       {
           "compilerOptions": {
               "module": "commonjs",
               "target": "ES2015",
               "sourceMap": true
           },
           "include": [
               "index.ts"
           ],
           "exclude": [
               "node_modules"
           ]
       }

5. also, you add this code in package.json

       // ...
       "dependencies": {
           "typescript": "^3.1.1"
       },
       "scripts": {
           "start": "node index.js",
           "prestart": "yarn tsc"
       },
       // ...

   1. if you wanna add tsc-watch --dev, yarn add tsc-watch --dev and write below code in package.json and tsconfig.json

          // package.json
          // ...
          "dependencies": {
              "typescript": "^3.1.1"
          },
          "scripts": {
              "start": "yarn tsc-watch --onSuccess \" node dist/index.js\" "
          },
          // ...

          // tsconfig.json
          {
              "compilerOptions": {
                  "module": "commonjs",
                  "target": "ES2015",
                  "sourceMap": true,
                  "outDir": "dist",
              },
              "include": [
                  "src/**/*"
              ],
              "exclude": [
                  "node_modules"
              ]
          }

   2. Before you start yarn, you have to make dir structure. ex) mkdir src and dist, also all ts file will exist src folder.

Typescript type && grammer

• assign parameter type

    const sayHi = (name:stirng, age:number, gender:string): string => {
    return `Hello ${name}, you are ${age}, you are the ${gender}!`;
    };

• assign object type in interface

    interface Human {
    name: string;
    age: number;
    gender: string;
    }
    const person = {
        name: "yesdoing",
        age: 28,
        gender: "male"
    };
    const sayHi = (person: Human): string => {
        return `Hello ${person.name}, you are ${person.age}, you are the ${person.gender}!`;
    };

• if you show interface in .js, you can use class.

    class Human {
    public name: string;
    public age: number;
    public gender: string;
    constructor(name: string, age: number, gender: string) {
        this.name = name;
        this.age = age;
        this.gender = gender;
        }
    }

    const yesdoing = new Human("yesdoing", 28, "male");