Repro

const names = ['a', 'b'];

const record = names.reduce(
  (accum, name) => ({
    ...accum,
    [name]: true,
  }),
  {} as Record<string, boolean>
);

Expected Result

Typo! It should be Record<string, boolean>, but because we're using a cast, it's missed. Ah, this does fire a TS error, thanks - updated the sample.

Also, u Using a cast is unnecessary because Array#reduce can take in a type parameter indicating the default value & return type. The above code would be better written as:

const names = ['a', 'b'];

const record = names.reduce<Record<string, boolean>>(
  (accum, name) => ({
    ...accum,
    [name]: true,
  }),
  {} 
);

Actual Result

No error.

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