javascript - 检查js函数中未定义的参数

Question

当非函数数据类型为时，我需要一些条件来捕获并抛出错误作为第二个参数传递。

包括未定义的传递？

function test(fn) {
  console.log(fn)
  // should throw an error if a non-function data type is 
  //passed as the second argument (includes undefined being passed)
  if (fn && typeof fn !== 'function') throw Error();
  return fn;
}


function demo() {}

test(); //undefined OK!

test(undefined); // SHOULD THROW ERROR ALSO

// throws error since argument is defined and not a function
test('sdfasfs'); 

Answer 1

区分隐式和显式传递 undefined 的唯一方法是查看传递了多少个参数:

function test(fn) {
  console.log(fn)
  // should throw an error if a non-function data type is 
  //passed as the second argument (includes undefined being passed)
  if (arguments.length > 0 && typeof fn !== 'function') throw Error();
  return fn;
}


function demo() {}

test(); //undefined OK!

test(undefined); // SHOULD THROW ERROR ALSO

// throws error since argument is defined and not a function
test('sdfasfs');