async function

  async function (param0) {
    statements
  }

  async function (param0, param1) {
    statements
  }

  async function (param0, param1, /* ... */ paramN) {
    statements
  }

  async function name(param0) {
    statements
  }

  async function name(param0, param1) {
    statements
  }

  async function name(param0, param1, /* ... */ paramN) {
    statements
  }

async (param) => expression;

async (param1, param2, ...paramN) => {
  statements;
};

function resolveAfter2Seconds(x) {
  return new Promise((resolve) => {
    setTimeout(() => {
      resolve(x);
    }, 2000);
  });
}

// async function   
const add = async function (x) {
  const a = await resolveAfter2Seconds(20);
  const b = await resolveAfter2Seconds(30);
  return x + a + b;
};

add(10).then((v) => {
  console.log(v); // 4  60 
});

// async function  IIFE 
(async function (x) {
  const p1 = resolveAfter2Seconds(20);
  const p2 = resolveAfter2Seconds(30);
  return x + (await p1) + (await p2);
})(10).then((v) => {
  console.log(v); // 2  60 
});