What is wrong with the following JavaScript code that uses async/await?

The code contains a syntax error because the keyword await is used outside of an async function. In JavaScript, await can only appear inside functions declared with the async keyword. The hello function is defined as a regular function, so the interpreter throws a SyntaxError when it encounters await. To fix the code, declare hello as an async function:

async function hello() {
  const x = await sayAfter2Seconds("Hello World");
  console.log(x);
}

Alternatively, you could wrap the call in an immediately invoked async function expression (IIFE):

(async () => {
  const x = await sayAfter2Seconds("Hello World");
  console.log(x);
})();

Once the await is inside an async context, the promise returned by sayAfter2Seconds will resolve after 2 seconds, and the string "Hello World" will be logged. The overall time complexity is O(1) because the function performs a constant amount of work regardless of input size.