Check Symbol.for exists in addition to Symbol before using it. #6324
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In some cases, Symbol may be shimmed but not Symbol.for. In those cases,
the existing code would throw on platforms with no native Symbol (IE11).
This change ensures
Symbol.for
exists before using it, preventing theissue.
We encountered this issue because of a deferred script partially shimming Symbol. After trying to load Apollo code asynchronously, IE11 would occasionally throw.
Checklist: