require-yields-check.md

require-yields-check

• Options
• Context and settings
• Failing examples
• Passing examples

Ensures that if a @yields is present that a yield (or yield with a value) is present in the function body (or that if a @next is present that there is a yield with a return value present).

Please also note that JavaScript does allow generators not to have yield (e.g., with just a return or even no explicit return), but if you want to enforce that all generators (except wholly empty ones) have a yield in the function body, you can use the ESLint require-yield rule. In conjunction with this, you can also use the checkGeneratorsOnly option as an optimization so that this rule won't need to do its own checking within function bodies.

Will also report if multiple @yields tags are present.

Options

• checkGeneratorsOnly - Avoids checking the function body and merely insists that all generators have @yields. This can be an optimization with the ESLint require-yield rule, as that rule already ensures a yield is present in generators, albeit assuming the generator is not empty). Defaults to false.
• next - If true, this option will insist that any use of a (non-standard) @next tag (in addition to any @yields tag) will be matched by a yield which uses a return value in the body of the generator (e.g., const rv = yield; or const rv = yield value;). This (non-standard) tag is intended to be used to indicate a type and/or description of the value expected to be supplied by the user when supplied to the iterator by its next method, as with it.next(value) (with the iterator being the Generator iterator that is returned by the call to the generator function). This option will report an error if the generator function body merely has plain yield; or yield value; statements without returning the values. Defaults to false.

Context and settings

Context	ArrowFunctionExpression, FunctionDeclaration, FunctionExpression
Tags	yields
Aliases	yield
Recommended	true
Options	checkGeneratorsOnly, contexts, exemptedBy, next

Failing examples

The following patterns are considered problems:

/**
 * @yields
 */
function * quux (foo) {

}
// Message: JSDoc @yields declaration present but yield expression not available in function.

/**
 * @yields
 */
function quux (foo) {

}
// "jsdoc/require-yields-check": ["error"|"warn", {"checkGeneratorsOnly":true}]
// Message: JSDoc @yields declaration present but yield expression not available in function.

/**
 * @next
 */
function quux (foo) {

}
// "jsdoc/require-yields-check": ["error"|"warn", {"checkGeneratorsOnly":true,"next":true}]
// Message: JSDoc @next declaration present but yield expression with return value not available in function.

/**
 * @next {SomeType}
 */
function * quux (foo) {

}
// "jsdoc/require-yields-check": ["error"|"warn", {"next":true}]
// Message: JSDoc @next declaration present but yield expression with return value not available in function.

/**
 * @next {SomeType}
 */
function * quux (foo) {
  yield;
}
// "jsdoc/require-yields-check": ["error"|"warn", {"next":true}]
// Message: JSDoc @next declaration present but yield expression with return value not available in function.

/**
 * @next {SomeType}
 */
function * quux (foo) {
  yield 5;
}
// "jsdoc/require-yields-check": ["error"|"warn", {"next":true}]
// Message: JSDoc @next declaration present but yield expression with return value not available in function.

/**
 * @yield
 */
function * quux (foo) {

}
// Settings: {"jsdoc":{"tagNamePreference":{"yields":"yield"}}}
// Message: JSDoc @yield declaration present but yield expression not available in function.

/**
 * @yield-returns {Something}
 */
function * quux (foo) {
  yield;
}
// Settings: {"jsdoc":{"tagNamePreference":{"next":"yield-returns"}}}
// "jsdoc/require-yields-check": ["error"|"warn", {"next":true}]
// Message: JSDoc @yield-returns declaration present but yield expression with return value not available in function.

/**
 * @yields {undefined} Foo.
 * @yields {String} Foo.
 */
function * quux () {

  yield foo;
}
// Message: Found more than one @yields declaration.

class Foo {
  /**
   * @yields {string}
   */
  * bar () {
  }
}
// Message: JSDoc @yields declaration present but yield expression not available in function.

/**
 * @yields
 */
function * quux () {

}
// Settings: {"jsdoc":{"tagNamePreference":{"yields":false}}}
// Message: Unexpected tag `@yields`

/**
 * @next
 */
function * quux () {

}
// Settings: {"jsdoc":{"tagNamePreference":{"next":false}}}
// "jsdoc/require-yields-check": ["error"|"warn", {"next":true}]
// Message: Unexpected tag `@next`

/**
 * @yields {string}
 */
function * f () {
  function * g() {
    yield 'foo'
  }
}
// Message: JSDoc @yields declaration present but yield expression not available in function.

/**
 * @yields {Promise<void>}
 */
async function * quux() {}
// Message: JSDoc @yields declaration present but yield expression not available in function.

/**
 * @yields {Promise<void>}
 */
const quux = async function * () {}
// Message: JSDoc @yields declaration present but yield expression not available in function.

/**
 * @yields {never} Foo.
 */
function * quux () {
  yield 5;
}
// Message: JSDoc @yields declaration set with "never" but yield expression is present in function.

/**
 * @next {never}
 */
function * quux (foo) {
  const a = yield;
}
// "jsdoc/require-yields-check": ["error"|"warn", {"next":true}]
// Message: JSDoc @next declaration set with "never" but yield expression with return value is present in function.

Passing examples

The following patterns are not considered problems:

/**
 * @yields Foo.
 */
function * quux () {

  yield foo;
}

/**
 * @yields {string} Foo.
 */
function * quux () {

  yield foo;
}

/**
 *
 */
function * quux () {
}

/**
 * @yields {undefined} Foo.
 */
function * quux () {}

/**
 * @yields { void } Foo.
 */
function quux () {}

/**
 * @yields Foo.
 * @abstract
 */
function * quux () {
  throw new Error('must be implemented by subclass!');
}

/**
 * @yields Foo.
 * @virtual
 */
function * quux () {
  throw new Error('must be implemented by subclass!');
}

/**
 * @yields Foo.
 * @constructor
 */
function * quux () {
}

/**
 * @interface
 */
class Foo {
  /**
   * @yields {string}
   */
  * bar () {
  }
}

/**
 * @record
 */
class Foo {
  /**
   * @yields {string}
   */
  * bar () {
  }
}
// Settings: {"jsdoc":{"mode":"closure"}}

/**
 * @yields {undefined} Foo.
 */
function * quux () {
}

/**
 * @yields {void} Foo.
 */
function * quux () {
}

/**
 * @yields {never} Foo.
 */
function * quux () {
}

/**
 * @yields {void} Foo.
 */
function * quux () {
  yield undefined;
}

/**
 * @yields {void} Foo.
 */
function * quux () {
  yield;
}

/**
 *
 */
function * quux () {
  yield undefined;
}

/**
 *
 */
function * quux () {
  yield;
}

/**
 * @yields {true}
 */
function * quux () {
  try {
    yield true;
  } catch (err) {
  }
  yield;
}

/**
 * @yields {true}
 */
function * quux () {
  try {
  } finally {
    yield true;
  }
  yield;
}

/**
 * @yields {true}
 */
function * quux () {
  try {
    yield;
  } catch (err) {
  }
  yield true;
}

/**
 * @yields {true}
 */
function * quux () {
  try {
    something();
  } catch (err) {
    yield true;
  }
  yield;
}

/**
 * @yields {true}
 */
function * quux () {
  switch (true) {
  case 'abc':
    yield true;
  }
  yield;
}

/**
 * @yields {true}
 */
function * quux () {
  switch (true) {
  case 'abc':
    yield;
  }
  yield true;
}

/**
 * @yields {true}
 */
function * quux () {
  for (const i of abc) {
    yield true;
  }
  yield;
}

/**
 * @yields {true}
 */
function * quux () {
  for (const a in b) {
    yield true;
  }
}

/**
 * @yields {true}
 */
function * quux () {
  for (let i=0; i<n; i+=1) {
    yield true;
  }
}

/**
 * @yields {true}
 */
function * quux () {
  while(true) {
    yield true
  }
}

/**
 * @yields {true}
 */
function * quux () {
  do {
    yield true
  }
  while(true)
}

/**
 * @yields {true}
 */
function * quux () {
  if (true) {
    yield;
  }
  yield true;
}

/**
 * @yields {true}
 */
function * quux () {
  if (true) {
    yield true;
  }
}

/**
 * @yields {true}
 */
function * quux () {
  var a = {};
  with (a) {
    yield true;
  }
}

/**
 * @yields {true}
 */
function * quux () {
  if (true) {
    yield;
  } else {
    yield true;
  }
  yield;
}

/**
 * @next {void}
 */
function * quux (foo) {

}
// "jsdoc/require-yields-check": ["error"|"warn", {"next":true}]

/**
 * @next {SomeType}
 */
function * quux (foo) {
  const a = yield;
}
// "jsdoc/require-yields-check": ["error"|"warn", {"next":true}]

/**
 * @next {SomeType}
 */
function * quux (foo) {
  const a = yield 5;
}
// "jsdoc/require-yields-check": ["error"|"warn", {"next":true}]

/**
 * @next {never}
 */
function * quux (foo) {

}
// "jsdoc/require-yields-check": ["error"|"warn", {"next":true}]