JavaScript中如何判断一个函数是同步函数，异步函数或者生成器函数？

Question

function a() {}
function* b() {}
async function c() {}
const d = () => {};
const e = async () => {};
function f(){
    return new Promise((resolve)=>{resolve(1)}
}
console.log(`a`, a,a.prototype);
console.log(`b`, b,b.prototype);
console.log(`c`, c,c.prototype);
console.log(`d`, d,d.prototype);
console.log(`e`, e,e.prototype);

console.log 可以显示是什么函数，但怎么通过代码识别？

Answer 1

function getTypeOfFunction(fn) {
  if (fn.constructor.name === 'AsyncFunction') {
    return 'Async Function';
  } else if (fn.constructor.name === 'GeneratorFunction') {
    return 'Generator Function';
  } else if (fn.constructor.name === 'Function' || fn.constructor.name === 'ArrowFunction') {
    return 'Sync Function';
  } else {
    return 'Not a function';
  }
}

function a() {}
function* b() {}
async function c() {}
const d = () => {};
const e = async () => {};

console.log(`a is a ${getTypeOfFunction(a)}`);
console.log(`b is a ${getTypeOfFunction(b)}`);
console.log(`c is a ${getTypeOfFunction(c)}`);
console.log(`d is a ${getTypeOfFunction(d)}`);
console.log(`e is a ${getTypeOfFunction(e)}`);

Answer 2

我以前是利用函数的 .toString() 方法，检查 async 是否存在：/^async/.test(func.toString())。