With 3.7 TypeScript's existing 'infer from usage' code fix became smarter. It will now use a list of known important types (string, number, array, Promise) and infer whether the usage of a type matches the API of these objects. For the next few examples, select the parameters of the functions, click the light bulb and choose "Infer Parameter types..." Infer a number array:

function pushNumber(arr) {
  arr.push(12);
}

// Infer a promise:

function awaitPromise(promise) {
  promise.then((value) => console.log(value));
}

// Infer the function, and its return type:

function inferAny(app) {
  const result = app.use("hi");
  return result;
}

function insertString(names) {
  names[1] = "hello";
}