Introduction

Debugging of JavaScript code in the main Electron process is usually done with the help of the node-inspector NodeJS module, which needs to be loaded in an Electron process in order to access code and resources within ASAR files. However, node-inspector has two dependencies that are native Node modules (v8-debug and v8-profiler), which must be rebuilt to target the Node runtime embedded in Electron. The Electron docs show one way to rebuild these modules:

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$ node_modules/.bin/node-pre-gyp --target=1.3.0 --runtime=electron --fallback-to-build --directory node_modules/v8-debug/ --dist-url=https://atom.io/download/atom-shell reinstall
$ node_modules/.bin/node-pre-gyp --target=1.3.0 --runtime=electron --fallback-to-build --directory node_modules/v8-profiler/ --dist-url=https://atom.io/download/atom-shell reinstall

Unfortunately as of Electron v1.3.0 rebuilding of the v8-profiler module will fail due to missing SetHiddenValue and GetHiddenValue methods in v8::Object. Electron ships with a newer version of V8 than NodeJS v6, and these particular methods were removed from recent versions of the V8 API. Eventually NodeJS will upgrade to the newer V8 API, NAN will be updated accordingly, and the v8-profiler module will be updated to address the breaking changes, but until then you’re going to have to install a modified version of the v8-profiler module that works with Electron.

Workaround

Replacing the original v8-profiler module with the modified version is easy, but locking in the replacement so that you don’t have to redo it every time you checkout a fresh copy of your project is a bit more finicky. Follow the steps below to lock in the correct version of the module, note that the first step assumes the current working directory is the directory containing your package.json.

  1. Replace the v8-profiler module in node-inspector:

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    cd node_modules/node-inspector
    npm install enlight/v8-profiler#v5.6.5-electron-v1.3 --save
    cd ../..

  2. Now there’s probably a redundant copy of the v8-profiler, remove it with npm prune. WARNING: This will clear out modules in node_modules that aren’t referenced in your package.json.

  3. Use the NPM shrinkwrap command to lock in the modified v8-profiler module:

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    npm shrinkwrap --dev

    Assuming no errors occured npm-shrinkwrap.json will be generated in the directory containing your package.json. If errors were encountered you will need to clear out any modules in node_modules that aren’t referenced in package.json and then try again. Once npm-shrinkwrap.json has been generated open it up and remove everything but the v8-profiler package info, the following is all that should be left:

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    {
      "name": "myapp",
      "version": "1.0.0",
      "dependencies": {
        "node-inspector": {
          "version": "0.12.8",
          "from": "node-inspector@>=0.12.8 <0.13.0",
          "resolved": "https://registry.npmjs.org/node-inspector/-/node-inspector-0.12.8.tgz",
          "dependencies": {
            "v8-profiler": {
              "version": "5.6.5",
              "from": "enlight/v8-profiler#v5.6.5-electron-v1.3",
              "resolved": "git://github.com/enlight/v8-profiler.git#607f871af2acf85ca75c3297b67989961699d7f5"
            }
          }
        }
      }
    }

    Add npm-shrinkwrap.json to source control so that the next time someone runs npm install after a fresh checkout NPM will install the correct version of v8-profiler.

  4. Rebuild the v8-profiler to target Electron using your method of choice.

You can probably cheat a bit and skip the first three steps above by creating npm-shrinkwrap.json manually, deleting node_modules/node-inspector, and then running npm install. Don’t forget to change the package name and version when you copy/paste the contents from step #3 into your npm-shrinkwrap.json.