Promise.all(), Promise.race(), and Promise.any()

Promise.all([
  Promise.resolve(1),
  Promise.resolve(2),
  {
    then(resolve) {
      resolve(3);
    }
  }
]).then(console.log);

Basic promise chaining
Thenables and promise coercion
This demonstrates thenable objects and promise coercion: 1) Promise.all accepts thenables, 2) Objects with then method are treated as promises, 3) Automatic conversion to proper promises, 4) Consistent with Promise resolution rules, 5) Enables custom promise-like objects, 6) Important for library interoperability.
Error handling
Promise composition