无法从json对象获取特定数据

{
  "name": "John",
  "age": 30,
  "city": "New York"
}

var obj = {
  "name": "John",
  "age": 30,
  "city": "New York"
};

var name = obj.name;
console.log(name); // 输出 "John"

var obj = {
  "first name": "John",
  "last name": "Doe",
  "age": 30,
  "city": "New York"
};

var firstName = obj["first name"];
console.log(firstName); // 输出 "John"

var propertyName = "age";
var age = obj[propertyName];
console.log(age); // 输出 30

var obj = {
  "name": "John",
  "age": 30,
  "city": "New York"
};

for (var key in obj) {
  var value = obj[key];
  console.log(key + ": " + value);
}

name: John
age: 30
city: New York