TypeScript compiler fails in ES5 environment

[arktronic]

The TypeScript compiler fails to run in the latest stable version of Jint (an ES5 environment) as of version 3.1 and above. The apparent issue is the use of Set, which does not exist prior to ES2015. Additional context tweet.

TypeScript Version: 3.2.2

Code

Executing the compiler in Jint issue reproduction

The repro app executes the same trivial compilation code against TypeScript 3.0.3, which works, and then 3.2.2, which fails. The failure occurs while executing the typescriptServices JS file itself, not while running the ts.transpileModule code.

Output from repro app:

--Works--
Result: var x = 'string';

--Fails--
Exception: ReferenceError: Set is not defined

Expected behavior:

Compiler executes successfully in Jint.

Actual behavior:

Jint throws an exception (see above for exception message).

[j-oliveras]

Git blame says that all uses of Set are from PR #26588 by @Andy-MS:
https://github.com/Microsoft/TypeScript/blob/fe1ba9bee37e54dad7a08d3d98c39d1e770e918f/src/compiler/inspectValue.ts#L41-L44

https://github.com/Microsoft/TypeScript/blob/fe1ba9bee37e54dad7a08d3d98c39d1e770e918f/src/compiler/inspectValue.ts#L107-L110

Note: I searched for "new Set" in all code.

[DanielRosenwasser]

Thanks everyone!