javascript - 问题使用键名访问 JSON 对象。但适用于 []

Question

使用 .给出错误但使用 [] 它有效吗？访问 JSON 对象键的正确语法是什么？

此语法给出错误:

var obj2G = obj.2G;

此语法有效，但为什么需要以这种方式访问​​？

var obj2G = obj["2G"];

var obj = {
  "2G": [{
    "essid": "SINGTEL-662F",
    "authmode": "psk psk2",
    "authkey": "0000026159",
    "isEnable": "1",
    "isHidden": "0",
    "hwaddr": "E0:8E:3C:00:66:30",
    "opmode": "ap"
  }, {
    "essid": "GUEST1-662F",
    "authmode": "psk psk2",
    "authkey": "aabbccddee",
    "isEnable": "0",
    "isHidden": "0",
    "hwaddr": "",
    "opmode": "ap"
  }, {
    "essid": "GUEST2-662F",
    "authmode": "psk psk2",
    "authkey": "aabbccddee",
    "isEnable": "0",
    "isHidden": "0",
    "hwaddr": "",
    "opmode": "ap"
  }, {
    "essid": "GUEST3-662F",
    "authmode": "psk psk2",
    "authkey": "aabbccddee",
    "isEnable": "0",
    "isHidden": "0",
    "hwaddr": "62:8E:3C:00:66:33",
    "opmode": "ap"
  }],
  "5G": [{
    "essid": "SINGTEL-662F(5G)",
    "authmode": "psk psk2",
    "authkey": "0000026159",
    "isEnable": "1",
    "isHidden": "0",
    "hwaddr": "E0:8E:3C:00:66:31",
    "opmode": "ap"
  }, {
    "essid": "GUEST1(5G)-662F",
    "authmode": "psk psk2",
    "authkey": "aabbccddee",
    "isEnable": "0",
    "isHidden": "0",
    "hwaddr": "6a:8e:3c:00:66:32",
    "opmode": "ap"
  }, {
    "essid": "GUEST2(5G)-662F",
    "authmode": "psk psk2",
    "authkey": "aabbccddee",
    "isEnable": "0",
    "isHidden": "0",
    "hwaddr": "",
    "opmode": "ap"
  }, {
    "essid": "GUEST3(5G)-662F",
    "authmode": "psk psk2",
    "authkey": "aabbccddee",
    "isEnable": "0",
    "isHidden": "0",
    "hwaddr": "6a:8e:3c:00:66:30",
    "opmode": "ap"
  }]
}

obj2G = obj["2G"];
console.log(obj2G);

obj2G = obj.2G;
console.log(obj2G);

Answer 1

如果您使用点符号:

property must be a valid JavaScript identifier, i.e. a sequence of alphanumerical characters, also including the underscore ("_") and dollar sign ("$"), that cannot start with a number. For example, object.$1 is valid, while object.1 is not.

在这种情况下，您必须使用括号表示法:

property_name is a string. The string does not have to be a valid identifier; it can have any value, e.g. "1foo", "!bar!", or even " " (a space).

请参阅文档:https://developer.mozilla.org/en/docs/Web/JavaScript/Reference/Operators/Property_accessors

值得一提的是，如果要使用变量访问属性，则必须使用括号表示法。例如:

var myName = "foo";
var myObject = { foo: 42};
console.log(myObject.myName);//returns undefined

但是:

var myName = "foo";
var myObject = { foo: 42};
console.log(myObject[myName]);//returns 42