TypeScript doesn't error on late definition/initialization of variables from outside an async closure.

TypeScript Version: 4.0-beta and Nightly (as of writing)

Search Terms: async closure variable initialization

Code

async function doSomething(): Promise<void> {
    const x = setTimeout(() => {
        const a = someVar + 1;
    }, 5000)

    await doSomethingSlowly();

    const someVar = 5;
}

Expected behavior:
There should be an error on const a = someVar + 1; since someVar may not have been initialized.

Actual behavior:
No error/warning with any settings that I could find.

Playground Link: link

Related Issues:

Comments
I see folks hit this every so often and it feels like something the TypeScript compiler could help warn against, in a similar way that 2448 and 2454 error.

从提供的 TypeScript Playground 复现开始，并将其行为与相关诊断 2448 和 2454 进行比较。确定编译器是否能够可靠地报告 someVar 可能在 async closure 中未初始化，然后根据示例和现有的相关案例验证任何诊断结果。