infer extracts the wrapped type from a generic container

What does this output?

// Simulate: type Unwrap<T> = T extends Array<infer E> ? E : T
// and:         type Awaited<T> = T extends Promise<infer R> ? Awaited<R> : T

function unwrapArray(arr) {
  if (Array.isArray(arr)) return arr[0];
  return arr;
}

function unwrapPromiseSync(p) {
  // Synchronously simulate what the type resolves to
  if (p && typeof p.then === 'function') {
    return 'Promise<' + typeof p._value + '>';
  }
  return typeof p;
}

// Unwrap<number[]>   => number (element type)
// Unwrap<string[]>   => string
// Unwrap<string>     => string (not an array, identity)

console.log(typeof unwrapArray([1, 2, 3]));    // number (element)
console.log(typeof unwrapArray(['a', 'b']));   // string (element)
console.log(typeof unwrapArray('hello'));      // string (not array — identity)
console.log(typeof unwrapArray([true, false])); // boolean

Correct Output

number
string
string
boolean

Why this output?

More Conditional Types Output Questions