Enable mocking of const

.travis.yml

@@ -4,6 +4,7 @@ node_js:
   - "0.12"
   - "4"
   - "5"
+  - "6"
 
 script:
   - npm test

README.md

@@ -139,9 +139,6 @@ myModule.__with__({
 Limitations
 -----------
 
-**Using `const`**<br>
-It's not possible to rewire `const` (see [#79](https://github.com/jhnns/rewire/issues/79)). This can probably be solved with [proxies](https://developer.mozilla.org/en/docs/Web/JavaScript/Reference/Global_Objects/Proxy) someday but requires further research. 
-
 **Transpilers**<br>
 Some transpilers, like babel, rename variables in order to emulate certain language features. Rewire will not work in these cases (see [#62](https://github.com/jhnns/rewire/issues/62)). A possible solution might be switching to [babel-plugin-rewire](https://github.com/speedskater/babel-plugin-rewire).
 
@@ -182,10 +179,15 @@ Please be aware that you can't rewire `eval()` or the global object itself.
 API
 ---
 
-### rewire(filename: String): rewiredModule
+### rewire(filename: String, [options]): rewiredModule
 
 Returns a rewired version of the module found at `filename`. Use `rewire()` exactly like `require()`.
 
+#### Options
+| Property | Default | Description |
+|----------|---------|-------------|
+| convertConst | false | Set to true to convert all `const` variables of the required module to `let`. This way you can mock const variables. **Caution**: Setting this to true can lead to inaccurate tests.
+
 ### rewiredModule.&#95;&#95;set&#95;&#95;(name: String, value: *): Function
 
 Sets the internal variable `name` to the given `value`. Returns a function which can be called to revert the change.

lib/index.js

@@ -7,10 +7,10 @@ var rewireModule = require("./rewire.js");
  * @param {!String} filename Path to the module that shall be rewired. Use it exactly like require().
  * @return {*} the rewired module
  */
-function rewire(filename) {
-    return rewireModule(module.parent, filename);
+function rewire(filename, opts) {
+    return rewireModule(module.parent, filename, opts);
 }
 
 module.exports = rewire;
 
-delete require.cache[__filename];   // deleting self from module cache so the parent module is always up to date
+delete require.cache[__filename];   // deleting self from module cache so the parent module is always up to date

lib/moduleEnv.js

@@ -2,6 +2,7 @@
 
 var Module = require("module"),
     fs = require("fs"),
+    babelCore = require("babel-core"),
     coffee;
 
     // caching original wrapper
@@ -11,18 +12,34 @@ var moduleWrapper0 = Module.wrapper[0],
     nodeRequire,
     currentModule;
 
-function load(targetModule) {
+function load(targetModule, isTransform) {
     nodeRequire = targetModule.require;
     targetModule.require = requireProxy;
     currentModule = targetModule;
 
     registerExtensions();
+
     targetModule.load(targetModule.id);
 
     // This is only necessary if nothing has been required within the module
     reset();
 }
 
+function compile(targetModule, src, filename) {
+    nodeRequire = targetModule.require;
+    targetModule.require = requireProxy;
+    targetModule.filename = filename;
+    currentModule = targetModule;
+
+    var convertedSrc = babelCore.transform(stripBOM(src), {
+        plugins: ["transform-es2015-constants"]
+    });
+
+    targetModule._compile(convertedSrc.code, filename);
+
+    reset();
+}
+
 function reset() {
     Module.wrapper[0] = moduleWrapper0;
     Module.wrapper[1] = moduleWrapper1;
@@ -91,4 +108,5 @@ try {
 }
 
 exports.load = load;
+exports.compile = compile;
 exports.inject = inject;

lib/rewire.js

@@ -1,5 +1,6 @@
 var Module = require("module"),
     fs = require("fs"),
+    path = require("path"),
     getImportGlobalsSrc = require("./getImportGlobalsSrc.js"),
     getDefinePropertySrc = require("./getDefinePropertySrc.js"),
     detectStrictMode = require("./detectStrictMode.js"),
@@ -8,11 +9,15 @@ var Module = require("module"),
 /**
  * Does actual rewiring the module. For further documentation @see index.js
  */
-function internalRewire(parentModulePath, targetPath) {
+function internalRewire(parentModulePath, targetPath, opts) {
     var targetModule,
         prelude,
         appendix,
-        src;
+        src,
+        isTransform;
+
+    opts = typeof opts === "object" ? opts : {};
+    isTransform = !!opts.convertConst;
 
     // Checking params
     if (typeof targetPath !== "string") {
@@ -54,7 +59,12 @@ function internalRewire(parentModulePath, targetPath) {
     }
 
     moduleEnv.inject(prelude, appendix);
-    moduleEnv.load(targetModule);
+
+    if(isTransform) {
+        moduleEnv.compile(targetModule, src, targetPath);
+    } else {
+        moduleEnv.load(targetModule);
+    }
 
     return targetModule.exports;
 }