为什么我的JavaScript函数不会结束？

Question

So I have the following code, from which I expect the x function to return null after being called 3 times but it keeps returning the the same function:

const repeat = (n, tailFn) => {
  for (let i = 0; i < n; i++) {
    tailFn = () => tailFn;
  }
  return tailFn;
};

const x = repeat(2, x => null);

console.log(x());           // function tailFn() { return _tailFn }
console.log(x()());         // function tailFn() { return _tailFn }
console.log(x()()()()()()); // function tailFn() { return _tailFn }

What am I doing wrong? See it on CodePen .

Answer 1

Your function just assigns () => tailFn to tailFn three times and then returns it. Instead, you should return a function which returns repeat(n - 1, tailFn) if n is not 0 , and tailFn otherwise.

 const repeat = (n, tailFn) => { return n !== 0 ? () => repeat(n - 1, tailFn) : tailFn; }; const x = repeat(2, x => null); console.log(x()); // () => repeat(n - 1, tailFn) console.log(x()()); // x => null console.log(x()()()); // null 

Answer 2

You have created a function that ALWAYS returns itself,

tailFn=()=>tailFn;

actually the loop is meaningless.Its behavior is similar to a recursive function without a base case.