Flow

# babel
yarn add --dev babel-cli babel-preset-flow
# flow
yarn add --dev flow-bin
# 初始化
flow init

yarn run flow

// .eslintrc.js
module.exports = {
  // extends: 'dwing',
  parser: 'babel-eslint',
  plugins: ['flowtype']
};

// .vscode/settings.json
// 将设置放入此文件中以覆盖默认值和用户设置。
{
  "javascript.validate.enable": false
}

"scripts": {
  "build": "babel src/ -d dist/",
  "prepublish": "yarn run build"
}

function square(n: number) {
  return n * n;
}

function stringifyBasicValue(value: string | number) {
  return '' + value;
}

// 避免使用 any
function getTypeOf(value: mixed): string {
  return typeof value;
}

function method(optionalValue?: string) {
  // ...
}

function foo({ x }: { x?: number } = {}): string {
  if (x) {
    return String(x);
  }
  return 'default string';
}