title: How to output only d.ts of my typescript project?
body: <p>For my typescript project, want to out <code>d.ts</code> file for entry file only:</p>
  
  <p>when i have a <strong>index.ts</strong>:</p>
  
  <pre><code>import a from './a';
  import b from './b';
  
  export default {
     a,
     b
  };
  </code></pre>
  
  <p>when i compile with ts with config <strong>tsconfig.json</strong>:</p>
  
  <pre><code>{
    "compilerOptions": {
      "outDir": "./lib",
      "declarationDir": "./build",
      "moduleResolution": "node",
      "strictNullChecks": true,
      "experimentalDecorators": true,
      "allowSyntheticDefaultImports": true,
      "noUnusedParameters": true,
      "noUnusedLocals": true,
      "noImplicitAny": true,
      "target": "es6",
      "declaration": true,
      "lib": [
        "dom",
        "es2015",
        "es2016",
      ],
    },
    "include": [
      "packages/index.ts",
      "typings"
    ],
    "exclude": [
      "node_modules",
      "**/__tests__",
      "**/__mocks__",
    ]
  }
  </code></pre>
  
  <p>would output tree file <strong>a.d.ts</strong>, <strong>b.d.ts</strong>, <strong>index.d.ts</strong></p>
  
  <p>how only output <strong>index.d.ts</strong></p>