动态 加载js，css文件

interface File {
  type: 'js'|'css';
  url: string;
}

type libKey = 'mtstatSdk'|'elementUI'|'weChatJSSDK';

const libMap: Record<libKey, {
  files: File[];
  loaded: boolean;
}> = {
  jsName: {
    files: [{
      type: 'js',
      url: 'xxx.js',
    }],
    loaded: false,
  },
  elementUI: {
    files: [{
      type: 'js',
      url: '//cdn.staticfile.org/element-ui/2.15.1/index.min.js',
    }, {
      type: 'css',
      url: '//cdn.staticfile.org/element-ui/2.15.1/theme-chalk/index.min.css',
    }],
    loaded: false,
  },
  weChatJSSDK: {
    files: [{
      type: 'js',
      url: 'https://res.wx.qq.com/open/js/jweixin-1.6.0.js',
    }],
    loaded: false,
  },
};

function loadJsFile(file: File): Promise<void> {
  return new Promise((resolve, reject) => {
    try {
      const script = document.createElement('script');
      script.src = file.url;
      script.onload = () => {
        resolve();
      };
      setTimeout(() => {
        reject(new Error(`Failed to load file: ${file.url}`));
      }, 3000);
      document.body.appendChild(script);
    } catch (e) {
      reject();
    }
  });
}

function loadCssFile(file: File): Promise<void> {
  return new Promise((resolve, reject) => {
    try {
      const link = document.createElement('link');
      link.setAttribute('rel', 'stylesheet');
      link.href = file.url;
      link.onload = () => {
        resolve();
      };
      document.body.appendChild(link);
    } catch (e) {
      reject();
    }
  });
}

// eslint-disable-next-line import/prefer-default-export
export async function ensure(libKey: libKey): Promise<void> {
  const lib = libMap[libKey];
  if (!lib) {
    throw new Error(`Invalid libKey: ${libKey}`);
  }
  if (lib.loaded === true) return;
  await Promise.all(
    lib.files.map(file => {
      if (file.type === 'js') {
        return loadJsFile(file);
      }
      if (file.type === 'css') {
        return loadCssFile(file);
      }
      return Promise.resolve();
    }),
  ).then(() => {
    lib.loaded = true;
  });
}