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

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 *.

Fixable: This rule is automatically fixable using the --fix flag on the command line.

Rule Details

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

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. If it is true, a space is required, otherwise spaces are disallowed.

    In anonymous function expressions, spacing between the * and the opening parenthesis is not checked. This is checked by the space-before-function-paren rule.

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

"generator-star-spacing": [2, {"before": false, "after": true}]

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"
"generator-star-spacing": [2, "after"]

When using {"before": true, "after": false} this placement will be enforced:

/*eslint generator-star-spacing: [2, {"before": true, "after": false}]*/
/*eslint-env es6*/

function *generator() {}

var anonymous = function *() {};

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

When using {"before": false, "after": true} this placement will be enforced:

/*eslint generator-star-spacing: [2, {"before": false, "after": true}]*/
/*eslint-env es6*/

function* generator() {}

var anonymous = function*() {};

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

When using {"before": true, "after": true} this placement will be enforced:

/*eslint generator-star-spacing: [2, {"before": true, "after": true}]*/
/*eslint-env es6*/

function * generator() {}

var anonymous = function *() {};

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

When using {"before": false, "after": false} this placement will be enforced:

/*eslint generator-star-spacing: [2, {"before": false, "after": false}]*/
/*eslint-env es6*/

function*generator() {}

var anonymous = function*() {};

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

To use this rule you must set the generators flag to true in the ecmaFeatures configuration object.

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