在 JavaScript 中将数据动态写入嵌套对象

Question

我想动态地将数据（以对象的形式）作为值写入嵌套在另一个对象中的对象；并动态创建键的名称（在循环内）。

我当前的代码如下所示：

data = {'x': 2, 'y': 3}

master_obj = {'useless': {}, 'important': {}}

var block_ind = 0
let trials = 12
let trials_per_block = 4
for (trial_ind=0; trial_ind<trials; trial_ind++) {
    // every 4 trials are in a new block
    block_ind = trial_ind % trials_per_block == 0 ? trial_ind/trials_per_block : block_ind
    
    master_obj['important']['block_0'+block_ind] = {}
    master_obj['important']['block_0'+block_ind]['trial_0'+trial_ind] = data
}
console.log(master_obj)

代码的输出如下所示（也可以在上面运行 sn-p）：

而预期的输出是[在一个块中进行多次试验，而不是一次]：

useless: {}
important:
    block_00:
        trial_00: {x: 2, y:3}
        trial_01: {x: 2, y:3}
        trial_02: {x: 2, y:3}
        trial_03: {x: 2, y:3}
    block_01:
        trial_04: {x: 2, y:3}
        trial_05: {x: 2, y:3}
        trial_06: {x: 2, y:3}
        trial_07: {x: 2, y:3}
    block_02:
        trial_08: {x: 2, y:3}
        trial_09: {x: 2, y:3}
        trial_10: {x: 2, y:3}
        trial_11: {x: 2, y:3}

感谢任何和所有的帮助和建议！

Answer 1

问题是你没有复制data，你只是在重复使用同一个对象。另一个问题是，当您尝试将另一个实例添加到现有块时，您会覆盖之前创建的对象。

如何复制它是一个潜在的复杂主题（请参阅this question's answers），但对于它自己的可枚举属性的浅拷贝，您可以使用扩展符号或 Object.assign 与对象文字，请参阅*** 下一行：

const data = {"x": 2, "y": 3}

const master_obj = {"useless": {}, "important": {}}

var block_ind = 0
let trials = 12
let trials_per_block = 4
const important = master_obj.important; // *** No need to repeat this
for (let trial_ind=0; trial_ind<trials; trial_ind++) {
//   ^^^−−−− *** Declare your variables
    // every 4 trials are in a new block
    block_ind = trial_ind % trials_per_block == 0 ? trial_ind/trials_per_block : block_ind

    // *** Only create this if it doesn't exist
    if (!important["block_0"+block_ind]) {
        important["block_0"+block_ind] = {}
    }
    important["block_0"+block_ind]["trial_0"+trial_ind] = {...data} // ***
}
console.log(master_obj)

另外请注意，我在data 和master_obj 上添加了const。如果没有let、const 或var，您的代码就会成为我所说的The Horror of Implicit Globals 的牺牲品。一定要声明你的变量。 （我建议始终使用const 或let，不要使用var。）

---

对于它的价值，您可以使用Math.floor(trial_ind / trials_per_block) 来确定块号。这是加上几个模板文字和其他具有描述性名称的常量：

const data = {"x": 2, "y": 3};

const master_obj = {"useless": {}, "important": {}};

const trials = 12;
const trials_per_block = 4;
const important = master_obj.important;
for (let trial_ind = 0; trial_ind < trials; ++trial_ind) {
    // Every 4 trials are in a new block
    const blockKey = `block_0${Math.floor(trial_ind / trials_per_block)}`;

    const trialKey = `trial_0${trial_ind}`;

    if (!important[blockKey]) {
        important[blockKey] = {};
    }
    important[blockKey][trialKey] = {...data};
}
console.log(master_obj);