eslint-plugin-void

This plugin enables the rules side-effect and arrow-body that can be used together or separately to enforce a style of using the void-operator.

The rules are entirely --fixable so you can enforce them at any time with little effort even in a large codebase.

Usage

Install package.

npm install eslint-plugin-void --save-dev

In .eslintrc

"plugins": [
  "void"
],
"rules": {
  "void/side-effect": {severity},
  "void/arrow-body": {severity}
}

Where severity is "error", "warn" or "off". You can omit "off" values.

side-effect

The void operator can be abused to write expressions that are nothing more than undefined with extra steps.

const isUndefined = value => value === void 0;

This rule disallows use of void without a possible side effect.

--fix

Code can be automatically fixed with --fix. The above example would be fixed to

const isUndefined = value => value === undefined;

If your code editor supports eslint suggestions, this rule will allow you to apply the fix through a suggestion.

Default

Examples of correct code for this rule

void functionCall();

void (object.field = value);

Examples of incorrect code for this rule

void 0;

void (() => functionCall());

allowTraps

The rule can be configured to allow arguments that may potentially trigger traps.

To allow all traps configure "allowTraps": true.

rules: {
  "void/side-effect": [{severity}, { "allowTraps": true }]
}

To allow select traps configure "allowTraps": {object}.

rules: {
  "void/side-effect": [
    {severity},
    {
      "allowTraps": {
        "get": {boolean},
        "has": {boolean},
        "ownKeys": {boolean}
      }
    }
  ]
}

You can omit false values from the configuration object.

Examples of correct code for this option

void object.field; // get

void 'field' in object; // has

void { ...object }; // ownKeys

arrow-body

The void operator can be used to stop arrow functions leaking return values.

const mutationCallback = value => void (object.field = value);

The same effect can be achieved with a function body.

const mutationCallback = value => { object.field = value; };

This rule enforces one or the other style.

--fix

Code can be automatically fixed with --fix. The above examples would be fixed to

const mutationCallback = value => {object.field = value;};

and

const mutationCallback = value => void (object.field = value);

respectively.

If your code editor supports eslint suggestions, this rule will allow you to apply the fixes through a suggestion.

Default

By default this rule prefers void in all cases.

Examples of correct code for this rule

(value => void sideEffect(value));

(value => void (object.field = value));

(value => void (sideEffect(value), object.field = value));

(value => {
  const input = value.trim();
  sideEffect(value);
});

(value => sideEffect(value));

Examples of incorrect code for this rule

(value => { sideEffect(value); });

(value => { object.field = value; });

(value => {
  sideEffect(value);
  object.field = value;
});

multi

The multi option allows you to define your preference for multiple side effects in an arrow function body.

Example of correct code for { "multi": "void" }

(value => void (sideEffect(value), object.field = value));

Example of incorrect code for { "multi": "void" }

(value => {
  sideEffect(value);
  object.field = value;
});

Example of correct code for { "multi": "body" }

(value => {
  sideEffect(value);
  object.field = value;
});

Example of incorrect code for { "multi": "body" }

(value => void (sideEffect(value), object.field = value));

{ multi: false }

Setting the multi option to false will disable this rule for multiple side effect expressions in an arrow function body.

single

The single option allows you to define your preference for a single side effect in an arrow function body.

Example of correct code for { "single": "void" }

(value => void sideEffect(value));

Example of incorrect code for { "single": "void" }

(value => {
  sideEffect(value);
});

Example of correct code for { "single": "body" }

(value => {
  sideEffect(value);
});

Example of incorrect code for { "single": "body" }

(value => void sideEffect(value));

{ single: false }

Setting the multi option to false will disable this rule for a single side effect in an arrow function body.

Prefer body

To configure this rule to always prefer function body over the void operator configure both single and multi.

rules: {
  "void/arrow-body": [{severity}, { "single": "body", "multi": "body" }]
}

When not to use this plugin

If you never want to use the void operator, use no-void instead. Even though this plugin offers fixes that no-void does not, the rules in this plugin conflict with no-void so use of both is discouraged.