Enforce spacing around the * in generator functions (generator-star-spacing)

The --fix option on the command line can automatically fix some of the problems reported by this rule.

Generators are a new type of function in ECMAScript 6 that can return multiple values over time. These special functions are indicated by placing an * after the function keyword.

Here is an example of a generator function:

/*eslint-env es6*/

function* generator() {
    yield "44";
    yield "55";
}

This is also valid:

/*eslint-env es6*/

function *generator() {
    yield "44";
    yield "55";
}

This is valid as well:

/*eslint-env es6*/

function * generator() {
    yield "44";
    yield "55";
}

To keep a sense of consistency when using generators this rule enforces a single position for the *.

Rule Details

This rule aims to enforce spacing around the * of generator functions.

Options

The rule takes one option, an object, which has two keys before and after having boolean values true or false.

• before enforces spacing between the * and the function keyword. If it is true, a space is required, otherwise spaces are disallowed.

  In object literal shorthand methods, spacing before the * is not checked, as they lack a function keyword.

• after enforces spacing between the * and the function name (or the opening parenthesis for anonymous generator functions). If it is true, a space is required, otherwise spaces are disallowed.

The default is {"before": true, "after": false}.

An example configuration:

"generator-star-spacing": ["error", {"before": true, "after": false}]

And the option has shorthand as a string keyword:

• {"before": true, "after": false} → "before"
• {"before": false, "after": true} → "after"
• {"before": true, "after": true} → "both"
• {"before": false, "after": false} → "neither"

An example of shorthand configuration:

"generator-star-spacing": ["error", "after"]

Additionally, this rule allows further configurability via overrides per function type.

• named provides overrides for named functions
• anonymous provides overrides for anonymous functions
• method provides overrides for class methods or property function shorthand

An example of a configuration with overrides:

"generator-star-spacing": ["error", {
    "before": false,
    "after": true,
    "anonymous": "neither",
    "method": {"before": true, "after": true}
}]

In the example configuration above, the top level "before" and "after" options define the default behavior of the rule, while the "anonymous" and "method" options override the default behavior. Overrides can be either an object with "before" and "after", or a shorthand string as above.

Examples

before

Examples of correct code for this rule with the "before" option:

/*eslint generator-star-spacing: ["error", {"before": true, "after": false}]*/
/*eslint-env es6*/

function *generator() {}

var anonymous = function *() {};

var shorthand = { *generator() {} };

after

Examples of correct code for this rule with the "after" option:

/*eslint generator-star-spacing: ["error", {"before": false, "after": true}]*/
/*eslint-env es6*/

function* generator() {}

var anonymous = function* () {};

var shorthand = { * generator() {} };

both

Examples of correct code for this rule with the "both" option:

/*eslint generator-star-spacing: ["error", {"before": true, "after": true}]*/
/*eslint-env es6*/

function * generator() {}

var anonymous = function * () {};

var shorthand = { * generator() {} };

neither

Examples of correct code for this rule with the "neither" option:

/*eslint generator-star-spacing: ["error", {"before": false, "after": false}]*/
/*eslint-env es6*/

function*generator() {}

var anonymous = function*() {};

var shorthand = { *generator() {} };

Examples of incorrect code for this rule with overrides present:

/*eslint generator-star-spacing: ["error", {
    "before": false,
    "after": true,
    "anonymous": "neither",
    "method": {"before": true, "after": true}
}]*/
/*eslint-env es6*/

function * generator() {}

var anonymous = function* () {};

var shorthand = { *generator() {} };

class Class { static* method() {} }

Examples of correct code for this rule with overrides present:

/*eslint generator-star-spacing: ["error", {
    "before": false,
    "after": true,
    "anonymous": "neither",
    "method": {"before": true, "after": true}
}]*/
/*eslint-env es6*/

function* generator() {}

var anonymous = function*() {};

var shorthand = { * generator() {} };

class Class { static * method() {} }

When Not To Use It

If your project will not be using generators or you are not concerned with spacing consistency, you do not need this rule.

Further Reading

• Understanding ES6: Generators

Version

This rule was introduced in ESLint 0.17.0.

Resources

• Rule source
• Documentation source