Understanding infer in TypeScript

TypeScript’s infer keyword, declared in the extends clause of a conditional type, captures a matched sub-type for use in the true branch, acting like type-level destructuring for function return types, array elements, and promise chains. The article connects it to built-in utilities ReturnType, Parameters, and Awaited, covers pitfalls around distributivity and variance, and explains constrained inference (infer X extends Constraint) available since TypeScript 4.7.