TypeScript can also infer the types of values returned by functions. It does this by looking at the types of the values after a function’s return statements.

function createGreeting(name: string) {
  return `Hello, ${name}!`;
}

const myGreeting = createGreeting('Aisle Nevertell');

Here’s how TypeScript can infer myGreeting above to be of type string:

1. createGreeting()’s return statement is followed by a string variable, so createGreeting() is inferred to return string.
2. createGreeting('Aisle Nevertell') therefore must result in a value of type string.
3. myGreeting is initialized to createGreeting('Aisle Nevertell'), which is a value with the type string.

Cool! Let’s see how this can help us fix bugs:

function ouncesToCups(ounces: number) {
  return `${ounces / 16} cups`;
}

const liquidAmount: number = ouncesToCups(3);
// Type 'string' is not assignable to type 'number'.

Here, TypeScript was able to infer that liquidAmount was being assigned a value of type string, despite it being declared as a variable of type number. This correctly results in an error being surfaced.