adds example of how to generate TypeScript type declaration files. Is…

…sue #24

examples/typedef-generation/README.md

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+This example shows how to generate TypeScript ".d.ts" files from .ts source files
+
+```
+$ ./build.js
+```
+
+Compiled .js bundle can now be found in `./out/` together with `main.d.ts`

examples/typedef-generation/build.js

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+#!/usr/bin/env node
+const { build, ts, tsconfig, dirname, glob, log } = require("estrella")
+
+build({
+  entry: "main.ts",
+  outfile: "out/foo.js",
+  onEnd(config) {
+    const dtsFilesOutdir = dirname(config.outfile)
+    generateTypeDefs(tsconfig(config), config.entry, dtsFilesOutdir)
+  },
+})
+
+function generateTypeDefs(tsconfig, entryfiles, outdir) {
+  const filenames = Array.from(
+    new Set(
+      (Array.isArray(entryfiles) ? entryfiles : [entryfiles])
+      .concat(tsconfig.include || []))).filter(v => v)
+  log.info("Generating type declaration files for", filenames.join(", "))
+  const compilerOptions = {
+    ...tsconfig.compilerOptions,
+    moduleResolution: undefined,
+    declaration: true,
+    outDir: outdir,
+  }
+  const program = ts.ts.createProgram(filenames, compilerOptions)
+  const targetSourceFile = undefined
+  const writeFile = undefined
+  const cancellationToken = undefined
+  const emitOnlyDtsFiles = true
+  program.emit(targetSourceFile, writeFile, cancellationToken, emitOnlyDtsFiles)
+  log.info("Wrote", glob(outdir + "/*.d.ts").join(", "))
+}

examples/typedef-generation/main.ts

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+export interface Named {
+  readonly name :string
+}
+
+export class Foo implements Named {
+  readonly name :string
+}
+
+export class Bar extends Foo {
+  readonly id :number
+  getName() :string {
+    return this.name
+  }
+}

examples/typedef-generation/test.sh

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+#!/bin/sh
+set -e
+rm -rf out
+./build.js -no-diag
+head -n3 out/main.d.ts

examples/typedef-generation/tsconfig.json

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+{
+  "compilerOptions": {
+    "noImplicitAny": true,
+    "strictFunctionTypes": true,
+    "strictBindCallApply": true,
+    "noImplicitThis": true,
+    "alwaysStrict": true,
+    "noUnusedLocals": true,
+    "noUnusedParameters": true,
+    "noFallthroughCasesInSwitch": true,
+    "noImplicitReturns": true,
+    // "strictNullChecks": true, "strictPropertyInitialization": true,
+    "moduleResolution": "node",
+    "target": "es2017",
+    "baseUrl": "src"
+  },
+  "include": [
+    "main.ts"
+  ]
+}