javascript - 检查关联数组中是否存在键

Question

告诉我，如何正确检查关联数组中键的存在？

例如:

var mydata = {
    key1: '',
    key2: {
        subkey1: {
            subkey1_1: {
                value1: ''
                value2" '',
            },
        },
        subkey2: '';
    },
}

if ((mydata.key2 != undefined) && (mydata.key2.subkey1 != undefined) && (mydata.key2.subkey1.subkey1_1 != undefined))
    mydata.key2.subkey1.subkey1_1.value1 = 'test';

太长且令人困惑

((mydata.key2 != undefined) && (mydata.key2.subkey1 != undefined) && (mydata.key2.subkey1.subkey1_1 != undefined))

我想使用一个更简单的函数，比如

safeSet(mydata.key2.subkey1.subkey1_1.value1, 'test');

或

if (is_undefined(mydata.key2.subkey1.subkey1_1.value1) == true)
    mydata.key2.subkey1.subkey1_1.value1 = 'test'; // now - error if 'mydata.key2.subkey1.subkey1_1' not exist

Answer 1

您可以使用 reduce() 创建自定义函数来测试嵌套属性是否存在。您可以将 key 作为字符串传递。

var mydata = {
  key1: '',
  key2: {
    subkey1: {
      subkey1_1: {
        value1: '',
        value2: '',
      },
    },
    subkey2: ''
  },
}

function safeSet(key, data) {
  return key.split('.').reduce(function(r, e) {
    return r ? r[e] : undefined;
  }, data) != undefined
}

console.log(safeSet('key2.subkey1.subkey1_1.value1', mydata))