Adding transformAsync

CHANGELOG.md

@@ -21,6 +21,7 @@
 - `[jest-reporters]` Add static filepath property to all reporters ([#11015](https://github.com/facebook/jest/pull/11015))
 - `[jest-snapshot]` [**BREAKING**] Make prettier optional for inline snapshots - fall back to string replacement ([#7792](https://github.com/facebook/jest/pull/7792))
 - `[jest-transform]` Pass config options defined in Jest's config to transformer's `process` and `getCacheKey` functions ([#10926](https://github.com/facebook/jest/pull/10926))
+- `[jest-transform]` Async code transformations ([#9889](https://github.com/facebook/jest/pull/9889))
 - `[jest-worker]` Add support for custom task queues and adds a `PriorityQueue` implementation. ([#10921](https://github.com/facebook/jest/pull/10921))
 - `[jest-worker]` Add in-order scheduling policy to jest worker ([10902](https://github.com/facebook/jest/pull/10902))
 

packages/babel-jest/src/index.ts

@@ -17,7 +17,7 @@ import * as fs from 'graceful-fs';
 import slash = require('slash');
 import type {
   TransformOptions as JestTransformOptions,
-  Transformer,
+  SyncTransformer,
 } from '@jest/transform';
 import type {Config} from '@jest/types';
 import {loadPartialConfig} from './loadBabelConfig';
@@ -26,7 +26,7 @@ const THIS_FILE = fs.readFileSync(__filename);
 const jestPresetPath = require.resolve('babel-preset-jest');
 const babelIstanbulPlugin = require.resolve('babel-plugin-istanbul');
 
-type CreateTransformer = Transformer<TransformOptions>['createTransformer'];
+type CreateTransformer = SyncTransformer<TransformOptions>['createTransformer'];
 
 const createTransformer: CreateTransformer = userOptions => {
   const inputOptions = userOptions ?? {};
@@ -160,7 +160,7 @@ const createTransformer: CreateTransformer = userOptions => {
   };
 };
 
-const transformer: Transformer<TransformOptions> = {
+const transformer: SyncTransformer<TransformOptions> = {
   ...createTransformer(),
   // Assigned here so only the exported transformer has `createTransformer`,
   // instead of all created transformers by the function

packages/jest-repl/src/cli/repl.ts

@@ -26,6 +26,12 @@ const evalCommand: repl.REPLEval = (
   let result;
   try {
     if (transformer) {
+      // TODO: support async as well
+      if (!transformer.process) {
+        throw new TypeError(
+          'Jest: currently only sync transforms are supported; a transform must export a `process function',
+        );
+      }
       const transformResult = transformer.process(
         cmd,
         jestGlobalConfig.replname || 'jest.js',