Add: constBindings option

README.md

@@ -82,7 +82,8 @@ const plugin = createPlugin(
   {
     include?: Array,
     exclude?: Array,
-    dynamicWrapper?: Function
+    dynamicWrapper?: Function,
+    constBindings?: Boolean
   } = {}
 );
 ```
@@ -119,6 +120,8 @@ const dynamicWrapper = (id) => {
 
 Virtual modules are always transformed.
 
+`constBindings` is a boolean. If true, the plugin will use `const` instead of `var` to declare the variable. This usually happens when you try to re-export the global variable. Default is false.
+
 Changelog
 ---------
 

index.d.ts

@@ -22,6 +22,11 @@ export type ExternalGlobalsOptions = {
    * [dynamicWrapper] is used to specify dynamic imports. It accepts a variable name and returns an expression
    */
   dynamicWrapper?: (variableName: VariableName) => string;
+
+  /**
+   * [constBindings] is used to decide whether to use `const` to declare variables. Default is `false`
+   */
+  constBindings?: boolean;
 };
 
 export declare function externalGlobals(

index.js

@@ -8,7 +8,7 @@ function isVirtualModule(id) {
   return id.startsWith("\0");
 }
 
-function createPlugin(globals, {include, exclude, dynamicWrapper = defaultDynamicWrapper} = {}) {
+function createPlugin(globals, {include, exclude, dynamicWrapper = defaultDynamicWrapper, constBindings = false} = {}) {
   if (!globals) {
     throw new TypeError("Missing mandatory option 'globals'");
   }
@@ -70,7 +70,8 @@ function createPlugin(globals, {include, exclude, dynamicWrapper = defaultDynami
       ast,
       code,
       getName,
-      getDynamicWrapper: dynamicWrapper
+      getDynamicWrapper: dynamicWrapper,
+      constBindings
     });
     return isTouched ? {
       code: code.toString(),

lib/import-to-globals.js

@@ -32,13 +32,13 @@ function makeGlobalName(prop, name) {
   return `${name}.${prop}`;
 }
 
-function writeSpecLocal(code, root, spec, name, tempNames) {
+function writeSpecLocal(code, root, spec, name, tempNames, constBindings) {
   if (spec.isOverwritten) return;
   // we always need an extra assignment for named export statement
   // https://github.com/eight04/rollup-plugin-external-globals/issues/19
   const localName = `_global_${makeLegalIdentifier(name)}`;
   if (!tempNames.has(localName)) {
-    code.appendRight(root.start, `const ${localName} = ${name};\n`);
+    code.appendRight(root.start, `${constBindings ? "const" : "var"} ${localName} = ${name};\n`);
     tempNames.add(localName);
   }
   if (spec.local.name === localName) {
@@ -72,7 +72,7 @@ function writeIdentifier(code, node, parent, name) {
   }
 }
 
-function analyzeExportNamed(node, code, getName, tempNames) {
+function analyzeExportNamed(node, code, getName, tempNames, constBindings) {
   if (node.declaration || !node.source || !node.source.value) {
     return false;
   }
@@ -82,7 +82,7 @@ function analyzeExportNamed(node, code, getName, tempNames) {
   }
   for (const spec of node.specifiers) {
     const globalName = makeGlobalName(spec.local.name, name);
-    writeSpecLocal(code, node, spec, globalName, tempNames);
+    writeSpecLocal(code, node, spec, globalName, tempNames, constBindings);
   }
   if (node.specifiers.length) {
     code.overwrite(node.specifiers[node.specifiers.length - 1].end, node.source.end, "}");
@@ -126,7 +126,7 @@ class ExportLeftHand {
   }
 }
 
-async function importToGlobals({ast, code, getName, getDynamicWrapper}) {
+async function importToGlobals({ast, code, getName, getDynamicWrapper, constBindings}) {
   await prepare();
   let scope = attachScopes(ast, "scope");
   const bindings = new Map;
@@ -139,7 +139,7 @@ async function importToGlobals({ast, code, getName, getDynamicWrapper}) {
     if (node.type === "ImportDeclaration") {
       isTouched = analyzeImport(node, bindings, code, getName, globals) || isTouched;
     } else if (node.type === "ExportNamedDeclaration") {
-      isTouched = analyzeExportNamed(node, code, getName, tempNames) || isTouched;
+      isTouched = analyzeExportNamed(node, code, getName, tempNames, constBindings) || isTouched;
     }
   }
 
@@ -160,7 +160,7 @@ async function importToGlobals({ast, code, getName, getDynamicWrapper}) {
       if (isReference(node, parent)) {
         if (bindings.has(node.name) && !scope.contains(node.name)) {
           if (parent.type === "ExportSpecifier") {
-            writeSpecLocal(code, topStatement, parent, bindings.get(node.name), tempNames);
+            writeSpecLocal(code, topStatement, parent, bindings.get(node.name), tempNames, constBindings);
           } else {
             writeIdentifier(code, node, parent, bindings.get(node.name));
           }

package.json

@@ -36,10 +36,12 @@
   "author": "eight04 <eight04@gmail.com>",
   "license": "MIT",
   "devDependencies": {
+    "@eslint/js": "^9.9.0",
     "@rollup/plugin-commonjs": "^26.0.1",
     "c8": "^10.1.2",
     "endent": "^2.1.0",
     "eslint": "^9.5.0",
+    "globals": "^15.9.0",
     "mocha": "^10.5.2",
     "rollup": "^4.18.0",
     "tempdir-yaml": "^0.3.0"

test/test.js

@@ -309,8 +309,8 @@ describe("main", () => {
         mud: "MUD"
       });
       assert.equal(code.trim(), endent`
-        const _global_FOO_foo = FOO.foo;
-        const _global_MUD_mud = MUD.mud;
+        var _global_FOO_foo = FOO.foo;
+        var _global_MUD_mud = MUD.mud;
 
         export { _global_FOO_foo as bar, _global_MUD_mud as mud };
       `);
@@ -327,7 +327,7 @@ describe("main", () => {
         foo: "FOO"
       });
       assert.equal(code.trim(), endent`
-        const _global_FOO_foo = FOO.foo;
+        var _global_FOO_foo = FOO.foo;
 
         export { _global_FOO_foo as bar, _global_FOO_foo as baz };
       `);
@@ -346,8 +346,8 @@ describe("main", () => {
         boo: "BOO",
       });
       assert.equal(code.trim(), endent`
-        const _global_BAK = BAK;
-        const _global_BOO = BOO;
+        var _global_BAK = BAK;
+        var _global_BOO = BOO;
 
         export { _global_BOO as BOO, _global_BAK as baz };
       `);
@@ -383,6 +383,22 @@ describe("main", () => {
           export {foo};
     `, async resolve => {
       const {output: {"entry.js": {code}}} = await bundle(resolve("entry.js"), {foo: "FOO"});
+      assert.equal(code.trim(), endent`
+        var _global_FOO = FOO;
+
+        export { _global_FOO as foo };
+      `);
+    })
+  );
+
+  it("constBindings", () =>
+    withDir(`
+      - entry.js: |
+          import foo from "foo";
+
+          export {foo};
+    `, async resolve => {
+      const {output: {"entry.js": {code}}} = await bundle(resolve("entry.js"), {foo: "FOO"}, undefined, {constBindings: true});
       assert.equal(code.trim(), endent`
         const _global_FOO = FOO;
 
@@ -401,7 +417,7 @@ describe("main", () => {
     `, async resolve => {
       const {output: {"entry.js": {code}}} = await bundle(resolve("entry.js"), {foo: "FOO"});
       assert.equal(code.trim(), endent`
-        const _global_FOO = FOO;
+        var _global_FOO = FOO;
 
         export { _global_FOO as bar, _global_FOO as foo };
       `);
@@ -418,7 +434,7 @@ describe("main", () => {
       const {output: {"entry.js": {code}}} = await bundle(resolve("entry.js"), {foo: "FOO"});
       assert.equal(code.trim(), endent`
         console.log(FOO);
-        const _global_FOO = FOO;
+        var _global_FOO = FOO;
 
         export { _global_FOO as foo };
       `);
@@ -521,7 +537,7 @@ describe("main", () => {
         }
       );
       assert.equal(code.trim(), endent`
-        const _global_BAR = BAR;
+        var _global_BAR = BAR;
 
         const bar = _global_BAR;
         console.log('foo');
@@ -563,7 +579,7 @@ describe("main", () => {
       assert.equal(code.trim(), endent`
       var entry = {};
 
-      const _global_BAR = BAR;
+      var _global_BAR = BAR;
 
       const { a } = _global_BAR;
       console.log(a);
@@ -609,7 +625,7 @@ describe("main", () => {
         }
       );
       assert.equal(code.trim(), endent`
-      const _global_BAR = BAR;
+      var _global_BAR = BAR;
 
       var foo = (val) => {
         const { a } = _global_BAR;