Question

我很想知道你是否可以使用标准for循环在for / in循环中放置for / in循环。在下面的例子中，我试图列出每个游戏对象的所有属性，但我没有得到预期的结果。我尝试过使用点符号和方括号，但似乎都不起作用。这是不可能的还是我在语法中忽略了一些简单的东西？

＆＃13;

var games = [{
    "name": "PCH Mystery Game",
    "maxScore": 50000,
    "levels": 4,
    "players": ["akshat", "joe", "dandan", "andrew"],
    "maps": {
      "1": 1,
      "2": 2,
      "3": 3,
      "4": 4
    }
  },
  {
    "name": "PCH Token Dash",
    "maxScore": 11500,
    "levels": 2,
    "players": ["andrew", "dandan", "matt", "mitchell", "hadi"],
    "maps": {
      "1": 1,
      "2": 2,
      "3": 3,
      "4": 4
    }
  },
  {
    "name": "PCH Balloon Drop",
    "maxScore": 500,
    "levels": 1,
    "players": [
      "akshat", "joe", "dandan", "dan", "mark", "nagesh", "jessie", "lou"
    ],
    "maps": {
      "1": 1,
      "2": 2,
      "3": 3,
      "4": 4
    }
  },
  {
    "name": "PCH Envelope Toss",
    "maxScore": 7000,
    "levels": 84,
    "players": ["akshat", "jessie", "joe", "andrew", "dandan"],
    "maps": {
      "1": 1,
      "2": 2,
      "3": 3,
      "4": 4
    }
  },
  {
    "name": "PCH Prize Patrol Race",
    "maxScore": 100000,
    "levels": 5,
    "players": [
      "akshat", "joe", "andrew", "dandan", "lou", "roberto", "jessie", "haim", "matt", "mitchell", "ian"
    ],
    "maps": {
      "1": 1,
      "2": 2,
      "3": 3,
      "4": 4
    }
  }
];

for (game in games) {
  document.write("game: " + games[game].name + "<br>");
  for (prop in game) {
    document.write("property name: " + prop + "<br>");
    document.write("property value: " + game[prop] + "<br>");
    document.write("property value: " + game.prop + "<br>");
  }
  document.write("<br>");
}

＆＃13;

Answer 1

从根本上说，是的，您可以使用嵌套的for-in循环。这不是代码中的问题。

for-in循环中的变量是属性名称（或键），而不是实际值。另外，for-in并不是循环数组的正确方法（尽管如果你尝试的话可以使它工作）。 See my answer here获取循环数组的方法列表。

在这种情况下，你可能会使用forEach或（在现代环境中）for-of或只是一个简单的for循环来通过数组的外部循环，然后一个for-in循环（在对象属性上）

games.forEach(function(game) {
    for (var prop in game) {
        console.log("property name: " + prop);
        console.log("property value: " + game[prop]);
    }
});

直播示例：

＆＃13;

var games = [{
    "name": "PCH Mystery Game",
    "maxScore": 50000,
    "levels": 4,
    "players": ["akshat", "joe", "dandan", "andrew"],
    "maps": {
      "1": 1,
      "2": 2,
      "3": 3,
      "4": 4
    }
  },
  {
    "name": "PCH Token Dash",
    "maxScore": 11500,
    "levels": 2,
    "players": ["andrew", "dandan", "matt", "mitchell", "hadi"],
    "maps": {
      "1": 1,
      "2": 2,
      "3": 3,
      "4": 4
    }
  },
  {
    "name": "PCH Balloon Drop",
    "maxScore": 500,
    "levels": 1,
    "players": [
      "akshat", "joe", "dandan", "dan", "mark", "nagesh", "jessie", "lou"
    ],
    "maps": {
      "1": 1,
      "2": 2,
      "3": 3,
      "4": 4
    }
  },
  {
    "name": "PCH Envelope Toss",
    "maxScore": 7000,
    "levels": 84,
    "players": ["akshat", "jessie", "joe", "andrew", "dandan"],
    "maps": {
      "1": 1,
      "2": 2,
      "3": 3,
      "4": 4
    }
  },
  {
    "name": "PCH Prize Patrol Race",
    "maxScore": 100000,
    "levels": 5,
    "players": [
      "akshat", "joe", "andrew", "dandan", "lou", "roberto", "jessie", "haim", "matt", "mitchell", "ian"
    ],
    "maps": {
      "1": 1,
      "2": 2,
      "3": 3,
      "4": 4
    }
  }
];

games.forEach(function(game) {
    for (var prop in game) {
        console.log("property name: " + prop);
        console.log("property value: " + game[prop]);
    }
});

＆＃13;

但是你有很多选择，特别是在现代环境中。例如：

for (const game of games) {
    for (const [prop, value] of Object.entries(game)) {
        console.log(`${prop} is ${value}`);
    }
}

...使用for-of，解构和Object.entries。

直播示例：

＆＃13;

var games = [{
    "name": "PCH Mystery Game",
    "maxScore": 50000,
    "levels": 4,
    "players": ["akshat", "joe", "dandan", "andrew"],
    "maps": {
      "1": 1,
      "2": 2,
      "3": 3,
      "4": 4
    }
  },
  {
    "name": "PCH Token Dash",
    "maxScore": 11500,
    "levels": 2,
    "players": ["andrew", "dandan", "matt", "mitchell", "hadi"],
    "maps": {
      "1": 1,
      "2": 2,
      "3": 3,
      "4": 4
    }
  },
  {
    "name": "PCH Balloon Drop",
    "maxScore": 500,
    "levels": 1,
    "players": [
      "akshat", "joe", "dandan", "dan", "mark", "nagesh", "jessie", "lou"
    ],
    "maps": {
      "1": 1,
      "2": 2,
      "3": 3,
      "4": 4
    }
  },
  {
    "name": "PCH Envelope Toss",
    "maxScore": 7000,
    "levels": 84,
    "players": ["akshat", "jessie", "joe", "andrew", "dandan"],
    "maps": {
      "1": 1,
      "2": 2,
      "3": 3,
      "4": 4
    }
  },
  {
    "name": "PCH Prize Patrol Race",
    "maxScore": 100000,
    "levels": 5,
    "players": [
      "akshat", "joe", "andrew", "dandan", "lou", "roberto", "jessie", "haim", "matt", "mitchell", "ian"
    ],
    "maps": {
      "1": 1,
      "2": 2,
      "3": 3,
      "4": 4
    }
  }
];

for (const game of games) {
    for (const [prop, value] of Object.entries(game)) {
        console.log(`${prop} is ${value}`);
    }
}

＆＃13;

Answer 2

比for(prop in games[game])更清晰

for (i in games) {
  var game = games[i];
  document.write("game: " + game.name + "<br>");
  for (prop in game) {
    document.write("property name: " + prop + "<br>");
    document.write("property value: " + game[prop] + "<br>");
  }
  document.write("<br>");
}

请注意，for...in通常不会在数组中使用，因为数组通常需要有一个订单而且for...in不一定会尊重订单。它还有一些按键，但for (i = 0; i < games.length; i++)没有任何问题，然后以同样的方式继续。

for / in循环中的for / in循环

2 个答案: