我的代碼似乎有效-但每個答案后都有一個“未定義”

每當我運行我的代碼時，我都會得到我想要的答案。但是，每個答案下都有“未定義”。知道如何解決和防止這種情況發生嗎？我不確定為什么會出現這種情況，因為它顯然給了我一個明確的價值？

萬一重要，Javascript 新手。

謝謝

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
))

uj5u.com熱心網友回復：

正如其他人指出的那樣，這是因為您要回傳 console.log 的輸出，然后是 console.logging 。由于在函式內部呼叫了 console.log，您會在日志中看到答案，而第二個只是列印 undefined，因為這就是函式回傳的內容。

但是你有一些不必要的代碼。看這個：

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
))

您可以在輸入陣列上使用 filter() 生成一個只有臟元素的新陣列，然后將該新陣列的長度除以初始陣列的長度，并將其與閾值進行比較。在我的單行函式中，我回傳真/假，這通常是我通常認為的函式的預期輸出。如果您想將其強制為友好值，您可以在函式本身中（我將在布林值上使用三元運算子）：

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
))

或者將函式和字串選擇分開：

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');

如果您使用此函式要做的只是生成一個顯示友好的字串，那么繼續將字串轉換放入函式中。但是如果你打算在某種決策中使用這個函式，那么 true/false 就是要走的路，因為以后你可以這樣說：

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

它使代碼更具可讀性。如果你將函式本身命名為dirty()——而不是checkAir()——那么你可以這樣寫：

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

uj5u.com熱心網友回復：

回傳后洗掉console.log

uj5u.com熱心網友回復：

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
))

uj5u.com熱心網友回復：

而不是回傳console.log(something)，而是回傳字串。否則console.log在呼叫函式時洗掉。

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)
);

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