TypeScript · Senior · Question 27 of 75

What changed about type predicate inference in TS 5.5?

const nums = [1, null, 2].filter(x => x !== null);

✓Correct answer: TS infers the predicate x is number, so nums is number[]
2filter now always returns never[] for mixed arrays
3Type predicates were removed in favor of assertion functions

Explanation

Previously nums was (number | null)[], and you had to write (x): x is number => x !== null. Now the compiler infers a predicate for simple functions if returning true really narrows the type.

What changed about type predicate inference in TS 5.5?

Explanation

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