babel/packages/babel-plugin-transform-es2015-modules-commonjs/src/index.js

import {
  isModule,
  rewriteModuleStatementsAndPrepareHeader,
  isSideEffectImport,
  buildNamespaceInitStatements,
  ensureStatementsHoisted,
  wrapInterop,
} from "@babel/helper-module-transforms";
import simplifyAccess from "@babel/helper-simple-access";

export default function({ types: t, template }, options) {
  const {
    loose,
    allowTopLevelThis,
    strict,
    strictMode,
    noInterop,

    // Defaulting to 'true' for now. May change before 7.x major.
    allowCommonJSExports = true,
  } = options;
  const moduleAssertion = template(`
    (function(){
      throw new Error("The CommonJS 'module' variable is not available in ES6 modules.");
    })();
  `);
  const exportsAssertion = template(`
    (function(){
      throw new Error("The CommonJS 'exports' variable is not available in ES6 modules.");
    })();
  `);
  const getAssertion = localName =>
    (localName === "module" ? moduleAssertion() : exportsAssertion())
      .expression;

  const moduleExportsVisitor = {
    ReferencedIdentifier(path) {
      const localName = path.node.name;
      if (localName !== "module" && localName !== "exports") return;

      const localBinding = path.scope.getBinding(localName);
      const rootBinding = this.scope.getBinding(localName);

      if (
        // redeclared in this scope
        rootBinding !== localBinding ||
        (path.parentPath.isObjectProperty({ value: path.node }) &&
          path.parentPath.parentPath.isObjectPattern()) ||
        path.parentPath.isAssignmentExpression({ left: path.node }) ||
        path.isAssignmentExpression({ left: path.node })
      ) {
        return;
      }

      path.replaceWith(getAssertion(localName));
    },

    AssignmentExpression(path) {
      const left = path.get("left");
      if (left.isIdentifier()) {
        const localName = path.node.name;
        if (localName !== "module" && localName !== "exports") return;

        const localBinding = path.scope.getBinding(localName);
        const rootBinding = this.scope.getBinding(localName);

        // redeclared in this scope
        if (rootBinding !== localBinding) return;

        const right = path.get("right");
        right.replaceWith(
          t.sequenceExpression([right.node, getAssertion(localName)]),
        );
      } else if (left.isPattern()) {
        const ids = left.getOuterBindingIdentifiers();
        const localName = Object.keys(ids).filter(localName => {
          if (localName !== "module" && localName !== "exports") return false;

          return (
            this.scope.getBinding(localName) ===
            path.scope.getBinding(localName)
          );
        })[0];

        if (localName) {
          const right = path.get("right");
          right.replaceWith(
            t.sequenceExpression([right.node, getAssertion(localName)]),
          );
        }
      }
    },
  };

  return {
    visitor: {
      Program: {
        exit(path) {
          // For now this requires unambiguous rather that just sourceType
          // because Babel currently parses all files as sourceType:module.
          if (!isModule(path, true /* requireUnambiguous */)) return;

          // Rename the bindings auto-injected into the scope so there is no
          // risk of conflict between the bindings.
          path.scope.rename("exports");
          path.scope.rename("module");
          path.scope.rename("require");
          path.scope.rename("__filename");
          path.scope.rename("__dirname");

          // Rewrite references to 'module' and 'exports' to throw exceptions.
          // These objects are specific to CommonJS and are not available in
          // real ES6 implementations.
          if (!allowCommonJSExports) {
            simplifyAccess(path, new Set(["module", "exports"]));
            path.traverse(moduleExportsVisitor, {
              scope: path.scope,
            });
          }

          let moduleName = this.getModuleName();
          if (moduleName) moduleName = t.stringLiteral(moduleName);

          const {
            meta,
            headers,
          } = rewriteModuleStatementsAndPrepareHeader(path, {
            exportName: "exports",
            loose,
            strict,
            strictMode,
            allowTopLevelThis,
            noInterop,
          });

          for (const [source, metadata] of meta.source) {
            const loadExpr = t.callExpression(t.identifier("require"), [
              t.stringLiteral(source),
            ]);

            let header;
            if (isSideEffectImport(metadata)) {
              header = t.expressionStatement(loadExpr);
            } else {
              header = t.variableDeclaration("var", [
                t.variableDeclarator(
                  t.identifier(metadata.name),
                  wrapInterop(path, loadExpr, metadata.interop) || loadExpr,
                ),
              ]);
            }
            header.loc = metadata.loc;

            headers.push(header);
            headers.push(...buildNamespaceInitStatements(meta, metadata));
          }

          ensureStatementsHoisted(headers);
          path.unshiftContainer("body", headers);
        },
      },
    },
  };
}