我的代码似乎有效 - 但每个答案后都有一个“未定义”

Question

每当我运行我的代码时，我都会得到我想要的答案。但是，每个答案下都有“未定义”。知道如何解决和防止这种情况发生吗？我不确定为什么会出现这种情况，因为它显然给了我一个明确的价值？

如果它很重要，JavaScript 新手。

谢谢

const checkAir = function (samples, threshold) {
  let numb = samples.length 
  let dirtyCount = ""


  for (let i = 0 ; i < samples.length ; i++) {
    if (samples[i] === 'dirty'){
      dirtyCount++
    }
  }
  if (dirtyCount / numb >= threshold){
    return console.log("Polluted")
  } else {
    return console.log("Clean")
  }
}

console.log(checkAir(
  ['clean', 'clean', 'dirty', 'clean', 'dirty', 'clean', 'clean', 'dirty', 'clean', 'dirty'],
  0.3
));


console.log(checkAir(
  ['dirty', 'dirty', 'dirty', 'dirty', 'clean'],
  0.25
));

console.log(checkAir(
  ['clean', 'dirty', 'clean', 'dirty', 'clean', 'dirty', 'clean'],
  0.9
))

Answer 1

正如其他人指出的那样，这是因为您要返回 console.log 的输出，然后是 console.logging 的输出。由于函数内部调用了 console.log，您在日志中看到了答案，而第二个只是打印 undefined，因为这就是函数返回的内容。

但是你有一些不必要的代码。看看这个：

const checkAir = (samples, threshold) => {
  return samples.filter(s=>s=='dirty').length / samples.length > threshold;
}

console.log(checkAir(
  ['clean', 'clean', 'dirty', 'clean', 'dirty', 'clean', 'clean', 'dirty', 'clean', 'dirty'],
  0.3
));


console.log(checkAir(
  ['dirty', 'dirty', 'dirty', 'dirty', 'clean'],
  0.25
));

console.log(checkAir(
  ['clean', 'dirty', 'clean', 'dirty', 'clean', 'dirty', 'clean'],
  0.9
))

您可以在输入数组上使用 filter() 来生成一个仅包含脏元素的新数组，然后将该新数组的长度除以初始数组的长度并将其与阈值进行比较。在我的单行函数中，我返回真/假，这通常是我通常认为的函数的预期输出。如果您想将其强制为友好值，您可以在函数本身中（我将在布尔值上使用三元运算符）：

const checkAir = (samples, threshold) => {
  let polluted = samples.filter(s=>s=='dirty').length / samples.length > threshold;
  return polluted ? 'Polluted' : 'Clean';
}

console.log(checkAir(
  ['clean', 'clean', 'dirty', 'clean', 'dirty', 'clean', 'clean', 'dirty', 'clean', 'dirty'],
  0.3
));


console.log(checkAir(
  ['dirty', 'dirty', 'dirty', 'dirty', 'clean'],
  0.25
));

console.log(checkAir(
  ['clean', 'dirty', 'clean', 'dirty', 'clean', 'dirty', 'clean'],
  0.9
))

或者将函数和字符串选择分开：

const checkAir = (samples, threshold) => {
  return samples.filter(s=>s=='dirty').length / samples.length > threshold;
}

let check = checkAir(
  ['clean', 'clean', 'dirty', 'clean', 'dirty', 'clean', 'clean', 'dirty', 'clean', 'dirty'],
  0.3
);
console.log(check ? 'Polluted' : 'Clean');


check = checkAir(
  ['dirty', 'dirty', 'dirty', 'dirty', 'clean'],
  0.25
);
console.log(check ? 'Polluted' : 'Clean');

check = checkAir(
  ['clean', 'dirty', 'clean', 'dirty', 'clean', 'dirty', 'clean'],
  0.9
);
console.log(check ? 'Polluted' : 'Clean');

如果您对这个函数所做的只是生成一个显示友好的字符串，那么继续将字符串转换放入函数中。但是如果你打算在某种决策中使用这个函数，那么 true/false 是要走的路，因为稍后你可以说这样的话：

dirty = checkAir(samples, threshold);
if(dirty) { /*what to do if dirty*/ }
else { /*what to do if clean*/ }

它使代码更具可读性。如果你将函数本身命名为dirty()——而不是checkAir()——那么你可以这样写：

if(dirty(samples, threshold)) { /*dirty response*/ }
else { /*clean response*/ }

Answer 2

返回后删除console.log

Answer 3

const checkAir = function(samples, threshold) {
  let numb = samples.length
  let dirtyCount = ""


  for (let i = 0; i < samples.length; i++) {
    if (samples[i] === 'dirty') {
      dirtyCount++
    }
  }
  if (dirtyCount / numb >= threshold) {
    return "Polluted"
  } else {
    return "Clean"
  }
}

console.log(checkAir(
  ['clean', 'clean', 'dirty', 'clean', 'dirty', 'clean', 'clean', 'dirty', 'clean', 'dirty'],
  0.3
));


console.log(checkAir(
  ['dirty', 'dirty', 'dirty', 'dirty', 'clean'],
  0.25
));

console.log(checkAir(
  ['clean', 'dirty', 'clean', 'dirty', 'clean', 'dirty', 'clean'],
  0.9
))

Answer 4

不返回console.log(something)，而是返回字符串。 否则在调用函数时删除console.log。

const checkAir = function (samples, threshold) {
  let numb = samples.length;
  let dirtyCount = "";
  for (let i = 0; i < samples.length; i++) {
    if (samples[i] === "dirty") {
       dirtyCount++;
    }
  }
  if (dirtyCount / numb >= threshold) {
     return "Polluted";
  } else {
     return "Clean";
  }
};

console.log(
  checkAir(
[
  "clean",
  "clean",
  "dirty",
  "clean",
  "dirty",
  "clean",
  "clean",
  "dirty",
  "clean",
  "dirty"
],
0.3
  )
);

console.log(checkAir(["dirty", "dirty", "dirty", "dirty", "clean"], 0.25));
console.log(
  checkAir(["clean", "dirty", "clean", "dirty", "clean", "dirty", "clean"], 0.9)
);