feat: Replace CJS require declarations with ESM imports

README.md

@@ -78,6 +78,22 @@ Watch this 5-minute video and learn how to migrate from CommonJS to ESM:
 
 Here you can see the transformations that `ts2esm` applies.
 
+### Require Statements
+
+Before:
+
+```ts
+const fs = require('node:fs');
+const path = require('path');
+```
+
+After:
+
+```ts
+import fs from 'node:fs';
+import path from 'path';
+```
+
 ### Import Declarations
 
 Before:

src/converter/convertFile.test.ts

@@ -28,4 +28,16 @@ describe('convertFile', () => {
 
     await expect(modifiedFile.getText()).toMatchFileSnapshot(snapshot);
   });
+
+  it('turns CJS require statements into ESM imports', async () => {
+    const projectDir = path.join(fixtures, 'require-import');
+    const projectConfig = path.join(projectDir, 'tsconfig.json');
+    const snapshot = path.join(projectDir, 'src', 'main.snap.ts');
+    const project = ProjectUtil.getProject(projectConfig);
+
+    const sourceFile = project.getSourceFile('main.ts')!;
+    const modifiedFile = convertFile(projectConfig, sourceFile, true);
+
+    await expect(modifiedFile.getText()).toMatchFileSnapshot(snapshot);
+  });
 });

src/converter/convertFile.ts

@@ -1,6 +1,7 @@
 import {SourceFile, SyntaxKind} from 'ts-morph';
 import {rewrite} from '../main.js';
 import {ProjectUtil} from '../util/ProjectUtil.js';
+import {replaceRequire} from './replaceRequire.js';
 
 export function convertFile(tsConfigFilePath: string, sourceFile: SourceFile, dryRun: boolean) {
   const filePath = sourceFile.getFilePath();
@@ -10,6 +11,15 @@ export function convertFile(tsConfigFilePath: string, sourceFile: SourceFile, dr
 
   let madeChanges: boolean = false;
 
+  // Update "require" variable assignments to "import" declarations
+  sourceFile.getVariableStatements().forEach(statement => {
+    const updatedRequire = replaceRequire(sourceFile, statement);
+    if (updatedRequire) {
+      madeChanges = true;
+    }
+  });
+
+  // Add explicit file extensions to imports
   sourceFile.getImportDeclarations().forEach(importDeclaration => {
     importDeclaration.getDescendantsOfKind(SyntaxKind.StringLiteral).forEach(stringLiteral => {
       const hasAttributesClause = !!importDeclaration.getAttributes();
@@ -20,10 +30,13 @@ export function convertFile(tsConfigFilePath: string, sourceFile: SourceFile, dr
         sourceFilePath: sourceFile.getFilePath(),
         stringLiteral,
       });
-      madeChanges ||= adjustedImport;
+      if (adjustedImport) {
+        madeChanges = true;
+      }
     });
   });
 
+  // Add explicit file extensions to exports
   sourceFile.getExportDeclarations().forEach(exportDeclaration => {
     exportDeclaration.getDescendantsOfKind(SyntaxKind.StringLiteral).forEach(stringLiteral => {
       const hasAttributesClause = !!exportDeclaration.getAttributes();
@@ -34,7 +47,9 @@ export function convertFile(tsConfigFilePath: string, sourceFile: SourceFile, dr
         sourceFilePath: filePath,
         stringLiteral,
       });
-      madeChanges ||= adjustedExport;
+      if (adjustedExport) {
+        madeChanges = true;
+      }
     });
   });
 

src/converter/replaceRequire.ts

@@ -0,0 +1,45 @@
+import {SourceFile, SyntaxKind, VariableStatement} from 'ts-morph';
+
+export function replaceRequire(sourceFile: SourceFile, statement: VariableStatement) {
+  // Get variable declaration
+  const declaration = statement.getDeclarations()[0];
+  if (!declaration) {
+    return false;
+  }
+
+  // Get call expression from variable declaration
+  // @see https://github.com/dsherret/ts-morph/issues/682#issuecomment-520246214
+  const initializer = declaration.getInitializerIfKind(SyntaxKind.CallExpression);
+  if (!initializer) {
+    return false;
+  }
+
+  // Verify that we have a "require" call
+  const identifier = initializer.getExpression().asKind(SyntaxKind.Identifier);
+  if (identifier?.getText() !== 'require') {
+    return false;
+  }
+
+  // Extract the argument passed to "require" and use its value
+  const requireArguments = initializer.getArguments();
+  const packageName = requireArguments[0];
+  if (!packageName) {
+    return false;
+  }
+
+  // Narrowing the argument down to its literal value
+  const packageNameLiteral = packageName.asKind(SyntaxKind.StringLiteral);
+  if (!packageNameLiteral) {
+    return false;
+  }
+
+  // Add import declaration
+  sourceFile.addImportDeclaration({
+    defaultImport: declaration.getName(),
+    moduleSpecifier: packageNameLiteral.getLiteralValue(),
+  });
+
+  // Remove the original "require" statement
+  statement.remove();
+  return true;
+}

src/test/fixtures/require-import/src/main.snap.ts

@@ -0,0 +1,4 @@
+import fs from "node:fs";
+import path from "path";
+fs.access('.', () => {});
+console.log(path.basename);

src/test/fixtures/require-import/src/main.ts

@@ -0,0 +1,5 @@
+const fs = require('node:fs');
+const path = require('path');
+
+fs.access('.', () => {});
+console.log(path.basename);

src/test/fixtures/require-import/tsconfig.json

@@ -0,0 +1,10 @@
+{
+  "compilerOptions": {
+    "esModuleInterop": true,
+    "forceConsistentCasingInFileNames": true,
+    "module": "NodeNext",
+    "skipLibCheck": true,
+    "strict": true,
+    "target": "ES2020"
+  }
+}