Question

函数，expensiveItem（菜单），应该返回数组中最昂贵的项目，饭菜。在这种情况下，它应该返回“Double Quarter Pounder with Cheese”。相反，它返回“Double Cheeseburger”。我的代码在哪里出错？

var item1 = {
  name: "Big Mac",
  price: 3.99,
  calories: 530
};
var item2 = {
  name: "Filet-O-Fish",
  price: 3.79,
  calories: 390
};
var item3 = {
  name: "Double Cheeseburger",
  price: 1.59,
  calories: 430
};
var item4 = {
  name: "Double Quarter Pounder with Cheese",
  price: 4.79,
  calories: 740
};
var item5 = {
  name: "Chicken McNuggets",
  price: 4.49,
  calories: 190
};

var meals = [item1, item2, item3, item4, item5];


function init() {
  var lowestCost = document.getElementById('cheapestItem');

  lowestCost.onclick = function() {
    cheapestItem(meals);
  }

  var highestCost = document.getElementById('highestCost');

  highestCost.onclick = function() {
    expensiveItem(meals);
  }

}

window.onload = init;


// return name of cheapest item on menu
function cheapestItem(menu) {
  var msg = document.getElementById('msg1'); // is this necessary? Code works fine without it...

  var cheapestItem = operation(menu, "less");
  msg1.innerHTML = "The cheapest item is " + cheapestItem;
}

// return name of most expensive item on menu
function expensiveItem(menu) {
  var msg = document.getElementById('msg2');

  var expensiveItem = operation(menu, "greater");
  msg2.innerHTML = "The most expensive item is " + expensiveItem;
}

//return result based on given comparator operator
function operation(menu, op) {
  var v1 = menu[0].price;
  var item;

  for (var i = 0; i < menu.length; i++) {
    var v2 = menu[i].price;


    if ((op == "less" && (v2 < v1)) ||
      (op == "greater" && (v2 > v1))) {
      result = v2;
      item = menu[i].name;
    }
  }
  console.log(item);
  return item;
}

<body>

  <input type="button" id="cheapestItem" value="Cheapest Item">
  </div>
  <p id="msg1">message 1</p>

  <input type="button" id="highestCost" value="Most Expensive Item">
  </div>
  <p id="msg2">message 2</p>
</body>

Answer 1

问题在这里：

if ((op == "less" && (v2 < v1)) || (op == "greater" && (v2 > v1)))

您只是在比较v1和v2，但如果条件满足，您还应该v1分配v2的值。

说明：

以下是循环中的值

3.99 3.99
3.99 3.79
3.99 1.59
3.99 4.79
4.79 4.49

如果您注意到，最后2次操作满足条件。所以你会得到后者。

＆＃13;

var item1 = {
  name: "Big Mac",
  price: 3.99,
  calories: 530
};
var item2 = {
  name: "Filet-O-Fish",
  price: 3.79,
  calories: 390
};
var item3 = {
  name: "Double Cheeseburger",
  price: 1.59,
  calories: 430
};
var item4 = {
  name: "Double Quarter Pounder with Cheese",
  price: 4.79,
  calories: 740
};
var item5 = {
  name: "Chicken McNuggets",
  price: 4.49,
  calories: 190
};

var meals = [item1, item2, item3, item4, item5];


function init() {
  var lowestCost = document.getElementById('cheapestItem');

  lowestCost.onclick = function() {
    cheapestItem(meals);
  }

  var highestCost = document.getElementById('highestCost');

  highestCost.onclick = function() {
    expensiveItem(meals);
  }

}

window.onload = init;


// return name of cheapest item on menu
function cheapestItem(menu) {
  var msg = document.getElementById('msg1'); // is this necessary? Code works fine without it...

  var cheapestItem = operation(menu, "less");
  msg1.innerHTML = "The cheapest item is " + cheapestItem;
}

// return name of most expensive item on menu
function expensiveItem(menu) {
  var msg = document.getElementById('msg2');

  var expensiveItem = operation(menu, "greater");
  msg2.innerHTML = "The most expensive item is " + expensiveItem;
}

//return result based on given comparator operator
function operation(menu, op) {
  var v1 = menu[0].price;
  var item;

  for (var i = 0; i < menu.length; i++) {
    var v2 = menu[i].price;

    if ((op == "less" && (v2 <= v1)) ||
      (op == "greater" && (v2 >= v1))) {
      result = v1 = v2;
      item = menu[i].name;
    }
  }
  console.log(item);
  return item;
}

＆＃13;

<body>

  <input type="button" id="cheapestItem" value="Cheapest Item">
  </div>
  <p id="msg1">message 1</p>

  <input type="button" id="highestCost" value="Most Expensive Item">
  </div>
  <p id="msg2">message 2</p>
</body>

＆＃13;

替代方式

在init中对数组进行排序。现在你不必循环来获得最小值和最大值。

注意：使用window.load = function的不良做法，您应该使用window.addEventListener('load', function)而不是

＆＃13;

var item1 = {
  name: "Big Mac",
  price: 3.99,
  calories: 530
};
var item2 = {
  name: "Filet-O-Fish",
  price: 3.79,
  calories: 390
};
var item3 = {
  name: "Double Cheeseburger",
  price: 1.59,
  calories: 430
};
var item4 = {
  name: "Double Quarter Pounder with Cheese",
  price: 4.79,
  calories: 740
};
var item5 = {
  name: "Chicken McNuggets",
  price: 4.49,
  calories: 190
};

var meals = [item1, item2, item3, item4, item5];
var OP_LESS = "less";
var OP_GREATER = "greater";

function init() {
  var lowestCost = document.getElementById('cheapestItem');

  lowestCost.onclick = function() {
    cheapestItem(meals);
  }

  var highestCost = document.getElementById('highestCost');

  highestCost.onclick = function() {
    expensiveItem(meals);
  }
  sortData();
}

function sortData(){
  meals.sort(function(a,b){
    return a.price > b.price ? 1 : a.price < b.price ? -1 : 0
  });
}

window.addEventListener('load', init);

// return name of cheapest item on menu
function cheapestItem(menu) {
  var msg = document.getElementById('msg1'); // is this necessary? Code works fine without it...

  var cheapestItem = operation(menu, OP_LESS);
  msg1.innerHTML = "The cheapest item is " + cheapestItem;
}

// return name of most expensive item on menu
function expensiveItem(menu) {
  var msg = document.getElementById('msg2');
  var expensiveItem = operation(menu, OP_GREATER);
  msg2.innerHTML = "The most expensive item is " + expensiveItem;
}

//return result based on given comparator operator
function operation(menu, op) {
  return (op === OP_LESS ? meals[0] : meals[meals.length-1]).name
}

＆＃13;

<body>

  <input type="button" id="cheapestItem" value="Cheapest Item">
  </div>
  <p id="msg1">message 1</p>

  <input type="button" id="highestCost" value="Most Expensive Item">
  </div>
  <p id="msg2">message 2</p>
</body>

＆＃13;

Answer 2

当您找到＆＃34;更大＆＃34;时，您总是与初始v1值进行比较。你应该将新值设置为var v1。

if ((op == "less" && (v2 < v1)) ||
    (op == "greater" && (v2 > v1))) {
    result = v2;
    v1=v2; //Set new greater/lower value
    item = menu[i].name;
}

Answer 3

我建议只使用一个变量来测试并返回

function operation(menu, op) {
    var price = menu[0].price,
        item = menu[0].name;

    for (var i = 0; i < menu.length; i++) {
        if (
            op === "less"    && menu[i].price < price ||
            op === "greater" && menu[i].price > price
        ) {
            price = menu[i].price;
            item = menu[i].name;
        }
    }
    console.log(item);
    return item;
}

＆＃13;

var item1 = {      name: "Big Mac",      price: 3.99,      calories: 530    };
var item2 = {      name: "Filet-O-Fish",      price: 3.79,      calories: 390    };
var item3 = {      name: "Double Cheeseburger",      price: 1.59,      calories: 430    };
var item4 = {      name: "Double Quarter Pounder with Cheese",      price: 4.79,      calories: 740
};
var item5 = {      name: "Chicken McNuggets",      price: 4.49,      calories: 190    };

var meals = [item1, item2, item3, item4, item5];

function init() {
  var lowestCost = document.getElementById('cheapestItem');
  lowestCost.onclick = function() {
    cheapestItem(meals);
  }

  var highestCost = document.getElementById('highestCost');

  highestCost.onclick = function() {
    expensiveItem(meals);
  }
}

window.onload = init;

// return name of cheapest item on menu
function cheapestItem(menu) {
  var msg = document.getElementById('msg1'); // is this necessary? Code works fine without it...

  var cheapestItem = operation(menu, "less");
  msg1.innerHTML = "The cheapest item is " + cheapestItem;
}

// return name of most expensive item on menu
function expensiveItem(menu) {
  var msg = document.getElementById('msg2');

  var expensiveItem = operation(menu, "greater");
  msg2.innerHTML = "The most expensive item is " + expensiveItem;
}

//return result based on given comparator operator
function operation(menu, op) {
  var price = menu[0].price,
      item = menu[0].name;

  for (var i = 0; i < menu.length; i++) {
    if (op == "less" && menu[i].price < price || op == "greater" && menu[i].price > price) {
      price = menu[i].price;
      item = menu[i].name;
    }
  }
  console.log(item);
  return item;
}

＆＃13;

  <input type="button" id="cheapestItem" value="Cheapest Item">
  <p id="msg1">message 1</p>
  <input type="button" id="highestCost" value="Most Expensive Item">
  <p id="msg2">message 2</p>

＆＃13;

比较函数的返回值不正确？

3 个答案:

说明：

替代方式