Avoid unnecessarily importing isType from graphql package (apollo…

…graphql#8891)

CHANGELOG.md

@@ -8,6 +8,9 @@
 
   [@benjamn](https://github.com/benjamn) in [#8862](https://github.com/apollographql/apollo-client/pull/8862)
 
+- Avoid importing `isType` from the `graphql` package internally, to prevent bundlers from including as much as 3.4kB of unnecessary code. <br/>
+  [@benjamn](https://github.com/benjamn) in [#8891](https://github.com/apollographql/apollo-client/pull/8891)
+
 ## Apollo Client 3.4.15
 
 ### Bug Fixes

src/utilities/globals/fix-graphql.ts

@@ -1,14 +1,14 @@
 // The ordering of these imports is important, because it ensures the temporary
 // process.env.NODE_ENV polyfill is defined globally (if necessary) before we
-// import { isType } from 'graphql'. The instanceOf function that we really care
+// import { Source } from 'graphql'. The instanceOf function that we really care
 // about (the one that uses process.env.NODE_ENV) is not exported from the
-// top-level graphql package, but isType uses instanceOf, and is exported.
+// top-level graphql package, but graphql/language/source uses instanceOf, and
+// has relatively few dependencies, so importing it here should not increase
+// bundle sizes as much as other options.
 import { remove } from 'ts-invariant/process';
-import { isType } from 'graphql';
+import { Source } from 'graphql';
 
 export function removeTemporaryGlobals() {
-  // Calling isType here just to make sure it won't be tree-shaken away,
-  // provided applyFixes is called elsewhere.
-  isType(null);
-  return remove();
+  // Using Source here here just to make sure it won't be tree-shaken away.
+  return typeof Source === "function" ? remove() : remove();
 }