Private Variables for JavaScript

Member variables preceded with underscore will now actually yield errors, bringing you one step closer to program correctness!

Oftentimes, developers precede some member variables with underscores to indicate that they are "private". However, the underscore itself is almost meaningless to all JavaScript interpreters, and as such, there is no way to know whether or not there was any illegal access to "private" variables.

With this ESLint plug-in, linting errors will be thrown whenever one tries to access private variables from outside of a class' methods.

Quick Start

# Step 1
$ npm install -g yo generator-private-variables

# Step 2
$ cd /path/to/project/new/or/old
# Be sure to change "/path/to/project/new/or/old" to an actual folder!

# Step 3: be sure that you have your existing project backed-up, just in case!
$ yo private-variables

Start typing out some code. Perhaps create a new class, access a private variables using this._somePrivateVariable, be it outside of a method, or inside of a method, etc.

Then, run:

npm run lint

If you've accessed a private variable outside of a class, you should actually see linting errors indicating just that!

If, prior to running yo private-variables, you already had a lint script defined in your package.json file, then you would instead run:

npm run lint2

Hooking it up to a text-editor

Since the private variable checker is an ESLint plug-in, then if you want to check for illegal private variable access as you type, then you can install an ESLint plug-in for your text editor.

Configuring

The private variable checker is an ESLint plugin, and, under npm, it is called eslint-plugin-private-variables. ESLint would interpret the name as private-variables, and you would tell ESLint to import it by supplying the following config:

// This is either inside a `.eslintconfig` file, or it's the value of a property by the name `"eslintConfig"` inside a `package.json` file.

{
  // ...
  "plugins": [
    // ...
    "private-variables"
  ],

  "rules": {
    // ...
    "private-variables/no-access": [2, "class-only"]
  }
}

If you want to lint against code that uses ES6/ES7/ES2015 classes, then you may want to switch to the babel-eslint parser.

// Again, this is either in `.eslintconfig` or a property of the name `"eslintConfig"` inside a `package.json` file.

{
  "parser": "babel-eslint"
}

And if you haven't done so, you may also consider installing babel-eslint by running npm install --save-dev babel-eslint.