javascript - for/in 循环内的 for/in 循环

Question

我很想知道您是否可以像使用标准 for 循环那样在 for/in 循环中放置一个 for/in 循环。在下面的示例中，我试图列出每个游戏对象的所有属性，但没有得到预期的结果。我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，还是我忽略了语法中的一些简单内容？

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>");
}

Answer 1

从根本上说，是的，您可以嵌套 for-in 循环。这不是您的代码中的问题。

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 不是循环遍历数组的正确方法(尽管如果您尝试的话可以使它工作)。 See my answer here获取循环遍历数组的方法列表。

在这种情况下，您可能会使用 forEach 或(在现代环境中)for-of 或者只是一个简单的 for 循环外层循环遍历数组，然后是一个 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]);
    }
});

实例:

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]);
    }
});

但是您有很多选择，尤其是在现代环境中。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 .

实例:

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}`);
    }
}