Get a way to represent iterable types while keeping ES5 compatiblity

[saschanaz]

TypeScript Version: 2.7.0-dev.201xxxxx

Search Terms:

Code

// Some standard web interfaces or third-party libraries support Symbol.iterator

interface SomeStandardInterface {
  method(iterable: Iterable<number>): void; // Error, no Iterable on lib.es5.d.ts
}

interface SomeThirdPartyInterface {
  [Symbol.iterator](): IterableIterator<number>; // Error, no Symbol, no IterableIterator
}

Expected behavior: We should provide a clean way to write iterable types on ES5-compatible type definition files.

Actual behavior: No such way. Some DefinitelyTyped definitions e.g. @types/node workaround this by defining Symbol.iterator and empty Iterable* interfaces.

Related Issues:

microsoft/TypeScript-DOM-lib-generator#419
#13031
#19806

[mhegazy]

Lib references is meant to address these issues.. unfortunately there is not an easy easy way to conditionally define a declaration. it is either there or not. at least with lib references the management of these dependencies will not involve the user.

Possibly related to #2900

[typescript-bot]

Automatically closing this issue for housekeeping purposes. The issue labels indicate that it is unactionable at the moment or has already been addressed.