不同的数组类型与访问方式，分支的不同类型

1.不同的数组类型与访问方式

console.log("-------// ! 1.数值(number)-------");
console.log(123, typeof 123);
console.log("-------//! 2.字符串(string)-------");
console.log("baidu.com", typeof "baidu.com");
console.log("-------//! 3.布尔(boolean)-------");
console.log(true, typeof true);
console.log("-------//! 4.undefined-------");
console.log(typeof a);
console.log("-------//! 5.null(不返回null,返回object)-------");
console.log(typeof null);
console.log("-------//! 6.数组(array)-------");
const arr = ["苹果", 10, "red"];
console.log("array: ", arr[0], arr[1], arr[2]);
// 判断: 不用typeof, 用 Array.isArray(arr)
console.log(typeof arr, Array.isArray(arr));
console.log("-------//! 7.对象(object)-------");
const item = {
  name: "苹果",
  price: 10,
  color: "red",
};
console.log("object: ", item.name, item.price, item.color);
console.log(typeof item);
console.log("-------//! 8.函数(function)-------");
function fn1() {}
// 匿名函数,用一个变量来引用
const fn2 = function () {};
// 箭头函数: 匿名函数的简写
const fn3 = () => {};
console.log(typeof fn1, typeof fn2, typeof fn3);
console.log("-------// ! 9.一维数组-------");
const arr1 = ["苹果", 10, "red"];
arr1.forEach(item => console.log(item));
console.log("-------// ! 10.多维数组-------");
const arr2 = [
  ["苹果", 10, "red"],
  ["梨", 12, "yellow"],
  ["香蕉", 6, "yello"],
];
arr2.forEach(item => console.log(item));
console.log("-------// ! 11.对象数组-------");
const arr3 = [
  { name: "苹果", price: 10, color: "red" },
  { name: "梨", price: 12, color: "yellow" },
  { name: "香蕉", price: 6, color: "yello" },
];
arr3.forEach(item => console.log(item));
console.log("-------// ! 12.类数组-------");
const arr4 = {
  0: "苹果",
  1: "梨",
  2: "香蕉",
  length: 3,
};
console.log(Array.from(arr4));

2.分支的不同类型

console.log("------// * 1. 单分支-------");
if (true) {
  console.log("success");
}
console.log("------// * 2. 双分支(简化: 三元)-------");
let status = !true;
if (status) {
  console.log("成功");
} else {
  console.log("失败");
}
// 三元进行简化
let result = status ? "成功" : "失败";
console.log(result);
console.log("------// * 3. 多分支(简化: switch)-------");
let grade = "E";
if (grade === "A") {
  console.log("优秀");
} else {
  if (grade === "B") {
    console.log("良好");
  } else {
    if (grade === "C") {
      console.log("合格");
    } else {
      if (grade === "D") {
        console.log("补考");
      } else {
        console.log("非法输入");
      }
    }
  }
}
//?switch
grade = "C";
switch (grade) {
  case "A":
    console.log("优秀");
    break;
  case "B":
    console.log("良好");
    break;
  case "C":
    console.log("合格");
    break;
  case "D":
    console.log("补考");
    break;
  default:
    console.log("非法输入");
    break;
}