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Description
TypeScript Version: 2.5.0
Code
const a: (d: string) => number = (d) => d.length;
const b: (d?: string) => number = a;
b();Expected behavior:
When compiled with --strict, the assignment of b should cause a type error along the lines of:
string | undefinedis not assignable to typestring.
Actual behavior:
The code compiles with --strict, then throws an exception at runtime on the expression d.length.
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DuplicateAn existing issue was already createdAn existing issue was already createdFixedA PR has been merged for this issueA PR has been merged for this issue