为什么我的脚本说 '(' === ')' 是真的？

Question

I was doing this kata on codewars. The question wants the function to return true if the first argument (string) passed in ends with the 2nd argument (also a string). So I wrote my function and everything worked just fine until it compares ':-)' with ':-(' and returns true.

What is wrong? I'm so confident that my code should work that I don't even know what to search for.

 function solution(str, ending){ if (!ending) return true; // if ending is a empty string return true (the question wants that) let ok; const strArr = str.split(''), endingArr = ending.split(''); for (let i = 0; i < endingArr.length; i++) strArr.reverse()[i] === endingArr.reverse()[i] ? ok = true : ok = false; return ok; } console.log(solution(":-)",":-("));

Answer 1

Your problem is a misunderstanding of what reverse() does. It does not return a reversed copy of the old array, it reverses the existing array and returns that same array. As a result, you keep reversing the arrays back and forth every iteration of the loop, causing some elements to be skipped and some to be checked twice.

Array.prototype.reverse() on MDN

Edit:

As pointed out by others in the comments, both to the question and this answer, there are in fact multiple problems.

reverse() aside, the loop always sets ok to the result of the last comparison, making the function ignore all previous results.

The easier way to implement this is to remove ok altogether. Instead, return false as soon as a mismatch is detected. If the function runs long enough to exit the loop, it means no mismatch was detected and true can be returned.

Edit 2:

Just as a friendly suggestion:

While both reverse() and ok are real issues with the code, I only noticed the first one the first time around due to the formatting of the code. The ok problem was off-screen due to the line being too long. As such, once I spotted the reverse() issue, I assumed that was it and didn't bother scrolling sideways to see the rest of the code.

I am not going to demand that you write your own code in a certain way, but if you format it properly, it allows others to read it more easily. In essence, you help us to more easily help you.

For instance, this line:

for (let i = 0; i < endingArr.length; i++) strArr.reverse()[i] === endingArr.reverse()[i] ? ok = true : ok = false;

...would have been significantly easier to read as...

for (let i = 0; i < endingArr.length; i++) {
  if(strArr.reverse()[i] === endingArr.reverse()[i])
    ok = true;
  else
    ok = false;
}

...or some variation thereof. Here, the problem is significantly more visible and obvious.

Answer 2

The other answer explains many of the mistakes you've made. I wanted to point out just how much you've over-thought your solution.

 function solution(str, ending){ if (ending === "") return true; // if ending is a empty string return true (the question wants that) return str.endsWith(ending); } console.log(solution(":-)",":-(")); console.log(solution("foo","")); console.log(solution("foo","bar")); console.log(solution("foobar","bar"));

Even my solution above is overengineered, str.endsWith("") always returns true. So this can be simplified further.

 function solution(str, ending){ return str.endsWith(ending); } console.log(solution(":-)",":-(")); console.log(solution("foo","")); console.log(solution("foo","bar")); console.log(solution("foobar","bar"));