TypeScript does not recognize URLSearchParams as iterable

Question

I am getting the following error trying to build a small TypeScript project with yarn & webpack:

TS2549: Type 'URLSearchParams' is not an array type or a string type or does not have a '[Symbol.iterator]()' method that returns an iterator.

I'm trying to use a Node built-in URLSearchParams object in a simple loop:

for (let [name, value] of searchParams) {
    //do stuff
}

The Node LTS version 12 docs show that the Symbol.iterator method exists. It works in the Node REPL.

I found a closed issue in the TypeScript repo from 2017 that supposedly resolved this error. But I also tried using searchParams.entries() and the validator did not recognize it as an available property. So it feels like my TypeScript has a very out-of-date definition for URLSearchParams. Maybe this is just a packaging issue but I don't know how to investigate further. The yarn.lock file shows appropriate node types:

"@types/node@^12":
  version "12.12.53"
  resolved "https://registry.yarnpkg.com/@types/node/-/node-12.12.53.tgz#be0d375933c3d15ef2380dafb3b0350ea7021129"
  integrity sha512-51MYTDTyCziHb70wtGNFRwB4l+5JNvdqzFSkbDvpbftEgVUBEE+T5f7pROhWMp/fxp07oNIEQZd5bbfAH22ohQ==

typescript@^3.9.7:
  version "3.9.7"
  resolved "https://registry.yarnpkg.com/typescript/-/typescript-3.9.7.tgz#98d600a5ebdc38f40cb277522f12dc800e9e25fa"
  integrity sha512-BLbiRkiBzAwsjut4x/dsibSTB6yWpwT5qWmC2OfuCg3GgVQCSgMs4vEctYPhsaGtd0AeuuHMkjZ2h2WG8MSzRw==

When I look at the local copies of the Typescript definition files I see the addition of Iterable-related properties in lib.dom.iterable.d.ts (as mentioned in that closed GitHub issue). Somehow those are being ignored.

I can rewrite my code to use searchParams.forEach() instead, but I'd like to understand what's going wrong anyway.

Answer 1

As the original post speculates, the additional definitions in lib.dom.iterable.d.ts are not being used. The project's TypeScript config in tsconfig.json has to reference that file:

"lib": [
  "dom",
  "dom.iterable",
  "es2019"
]

With this, TypeScript now understands iterator-related properties for URLSearchParams and about 50 other types referenced in that file. I assume the separation is related to TypeScript backwards compatibility with older ECMAScript flavors, but I don't know.