在javascript中，测试深度嵌套在对象图中的属性? [英] In javascript, test for property deeply nested in object graph?

问题描述

我从 CouchDB 数据库中收集了一组不同的复杂 JSON 对象.每个都包含许多级别的嵌套属性——例如，

I've got a collection of disparate, complex JSON objects from a CouchDB database. Each contains many levels of nested properties--for example,

tps_report.personnel_info.productivity.units_sold = 8  

我想遍历这些对象并用它们做一些事情:例如，

I want to iterate through these objects and do stuff with them: for instance,

// writes units sold from each TPS report:
for (i in tpsReports) {
  if (tpsReports[i].personnel_info.productivity.units_sold < 10) {
    fireEmployee();
  }
}

问题是许多 TPS 报告没有设置所有这些属性.因此，如果我尝试这样做，当循环第一次到达没有personnel_info"属性的报告时，我会得到一个错误，从而尝试找到undefined"的productivity"属性.我宁愿发生的是条件只是跳过它并继续.

The problem is that many TPS reports don't have all these properties set. So if I try this, I'll get an error the first time the loop gets to a report without the "personnel_info" property and thus tries to find the "productivity" property of "undefined." What I'd rather happen is that the conditional just skips it and continues.

我看到了两种解决方法，这两种方法在我看来都很丑

I see two ways around this, both of which seem ugly to me

1. 使用嵌套条件分别测试每个属性
2. 将该行括在 try/catch 块中以捕获错误并忽略它

我更喜欢 PHP 的 isset() 函数之类的东西，无论您提供什么，它都不会抛出错误——它只会告诉您您要查找的特定变量是否存在或不是.所以，喜欢

What I'd prefer would be something like PHP's isset() function, which won't throw an error regardless of what you feed it--it'll just tell you whether the particular variable you're looking for exists or not. So, like

// writes units sold from each TPS report:
for (i in tpsReports) {
  if (isset(tpsReports[i].personnel_info.productivity.units_sold)){
    if (tpsReports[i].personnel_info.productivity.units_sold < 10) {
      fireEmployee();
    }
  }
}

有什么想法吗?

推荐答案

function isset(obj, propStr) {
    var parts = propStr.split(".");
    var cur = obj;
    for (var i=0; i<parts.length; i++) {
        if (!cur[parts[i]])
            return false;
        cur = cur[parts[i]];
    }
    return true;
}

请注意，第二个参数是一个字符串，因此在访问不存在的属性上的属性时不会引发异常.

Note that the second parameter is a string, so the exception doesn't get thrown when accessing a property on a nonexistent property.

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