使用JavaScript中的值获取属性

var obj = { name: "John", age: 30 };
console.log(obj.name); // 输出 "John"

var obj = { "first name": "John", "last name": "Doe" };
console.log(obj["first name"]); // 输出 "John"

var obj = { name: "John", age: 30 };
var propName = "name";
console.log(obj[propName]); // 输出 "John"

var obj = { name: "John", age: 30 };
var keys = Object.keys(obj);
console.log(keys); // 输出 ["name", "age"]

var arr = [1, 2, 3];
console.log(arr[0]); // 输出 1