TypeScript transformer to remove .js from import and export statements

webpack.config.js

// https://github.com/Microsoft/TypeScript/issues/16577#issuecomment-343699395

const path = require('path');
const ts = require('typescript');
const { isImportDeclaration, isExportDeclaration, isStringLiteral } = require('tsutils/typeguard/node');

function getCustomTransformers() {
    return { before: [stripJsExt] }

    function stripJsExt(context) {
        return sourceFile => visitNode(sourceFile);

        function visitNode(node) {
            if ((isImportDeclaration(node) || isExportDeclaration(node)) &&
                node.moduleSpecifier && isStringLiteral(node.moduleSpecifier)) {
                const targetModule = node.moduleSpecifier.text;
                if (targetModule.endsWith('.js')) {
                    const newTarget = targetModule.slice(0, targetModule.length - 3);
                    return isImportDeclaration(node) ?
                        ts.updateImportDeclaration(
                            node,
                            node.decorators,
                            node.modifiers,
                            node.importClause,
                            ts.createLiteral(newTarget)
                        ) :
                        ts.updateExportDeclaration(
                            node,
                            node.decorators,
                            node.modifiers,
                            node.exportClause,
                            ts.createLiteral(newTarget)
                        );
                }
            }
            return ts.visitEachChild(node, visitNode, context);
        }
    }
}

module.exports = {
    entry: './src/index.ts',
    output: {
        path: path.resolve(__dirname, 'dist'),
        filename: 'app.bundle.js'
    },
    resolve: {
        extensions: ['.ts', '.tsx', '.js', '.json']
    },
    module: {
        rules: [
            { test: /\.tsx?$/, loader: 'ts-loader', options: { getCustomTransformers } }
        ]
    }
};

@AviVahl no no, you understood correctly.
I've managed to code this piece, which deletes imports included in an inputted array.

if (ts.isNamedImports(node)) {
  const namedImports = node as ts.NamedImports;
  const newElements = namedImports.elements.filter(
    v => !decoratorNames.includes(v.name.text)
  );
  
  ts.updateNamedImports(namedImports, newElements);
}

Seems good to you?
I'd also like to entirely remove the import if newElements.length === 0, but I wasn't able to do it.

I've managed to do it, but maybe there is a cleaner way. Basically I save the ImportDeclaration reference and later I look for it.
The complete code is

export default (decorators: string[]) => {
  const importDeclarationsToRemove = [] as ts.ImportDeclaration[];

  const updateNamedImports = (node: ts.NamedImports) => {
    const newElements = node.elements.filter(v => !decorators.includes(v.name.getText()));

    if (newElements.length > 0) {
      ts.updateNamedImports(node, newElements);
    } else {
      importDeclarationsToRemove.push(node.parent.parent);
    }
  };

  const createVisitor = (
    context: ts.TransformationContext
  ): ((node: ts.Node) => ts.VisitResult<ts.Node>) => {
    const visitor: ts.Visitor = (node: ts.Node): ts.VisitResult<any> => {
      // Remove Decorators from imports
      if (ts.isNamedImports(node)) {
        updateNamedImports(node);
      }

      // Remove Decorators applied to elements
      if (ts.isDecorator(node)) {
        const decorator = node as ts.Decorator;
        const identifier = decorator.getChildAt(1) as ts.Identifier;

        if (decorators.includes(identifier.getText())) {
          return undefined;
        }
      }

      const resultNode = ts.visitEachChild(node, visitor, context);
      const index = importDeclarationsToRemove.findIndex(id => id === resultNode);

      if (index !== -1) {
        importDeclarationsToRemove.splice(index, 1);
        return undefined;
      }

      return resultNode;
    };

    return visitor;
  };

  return (context: ts.TransformationContext) => (sourceFile: ts.SourceFile) =>
    sourceFile.fileName.endsWith('component.ts')
      ? ts.visitNode(sourceFile, createVisitor(context))
      : sourceFile;
};

you can update the sourceFile's statements field... filtering out top level imports/exports you want to filter.
I've got several cool transformers (in several patterns) implemented here: https://github.com/AviVahl/ts-tools/tree/master/packages/robotrix
might be useful for reference.

@AviVahl Thanks! So you're saying I can simply .statements.filter(...) inside the visitor?

you need to ts.updateSourceFile with the filtered statements, but yes.

@AviVahl understood. Thanks again for the useful advices!