Intersection of features in modular lib files

[T-Hugs]

TypeScript Version: 2.0.3

It is very unclear how to effectively use the --lib compiler option. It appears there is a default set of libs that are included (i.e. when no --lib is specified). If any libs are specified with --lib, then it seems this default set gets replaced with the set you provide. I haven't been able to find any documentation on exactly what is in the default set.

Here's the issue I'm running into. I want to use the [default set] + es2015.collection. I've tried a number of things.

• --lib es2015.collection OR --lib es6 - Lots of errors because DOM isn't declared
• --lib es6,dom,scripthost,webworker - Several errors about duplicate signatures and declarations, e.g.
  lib.dom.d.ts(2145,5): error TS2375: Build: Duplicate number index signature.
lib.dom.d.ts(3772,14): error TS2403: Build: Subsequent variable declarations must have the same type. Variable 'srcElement' must be of type 'any', but here has type 'Element'.
• [no --lib option] - Can't use ES6 sets/maps.

Expected behavior:
Either the set of libs you can import needs to be disjoint, or the compiler should be able to handle duplicate declarations in these files.

[mhegazy]

The defaults are:

• if --target ES5 => dom,es5,scripthost
• if --target ES6 => dom,es6,dom.iterable,scripthost

Some notes,

• webworker is for WebWorker environments, these do not have DOM. so mixing dom and webworker do not make much sense.
• scripthost is for windows scripting host libraries. if you are not writing a windows script or a website that uses ActiveXObject, then no need for this.

[mhegazy]

Update the documentation in https://github.com/Microsoft/TypeScript-Handbook/blob/master/pages/Compiler%20Options.md to add this conent

[T-Hugs]

Thanks @mhegazy. There's one instance in our source where importScripts is used. When I don't specify --lib, it compiles fine. When I add --lib dom,es5,scripthost I get this error:
DiscussionRenderer.ts(130,33): error TS2304: Build: Cannot find name 'importScripts'.

Also, just a nit, the default values you added should go in the Default column on the markdown page :)

[T-Hugs]

Also, you said for es6 targets, dom.iterable is one of the default libs. Did you mean es2015.iterable?

[kitsonk]

Also, you said for es6 targets, dom.iterable is one of the default libs. Did you mean es2015.iterable?

It isn't a mistake. lib=es6 includes the es2015.iterable, but there are some DOM interfaces that are exposed as iterables in a ES6 compliant host, therefore dom.iterable.

[mhegazy]

here's one instance in our source where importScripts is used.

yes. the import script is more of an anomaly. it should not have been ever added to the library. but it is kept there for back compat purposes. so it was intentionally omitted.

[bborowin]

importScripts is a part of web worker functionality -- how else is it possible to include scripts (eg, lodash)??

[mhegazy]

if you are using web workers use --lib webworkers