class类与extends,super等的用法与字符串,数组常用API

1.class类与extends,super等的用法

let User = class {
  // 构造函数：声明属性
  constructor(uname, email) {
    // 1.属性
    this.uname = uname;
    this.email = email;
  }
  //   2.方法
  say() {
    return `${this.uname}:(${this.email})`;
    }
  //   3.静态成员
  static nation = "CN";
};
const user = new User("libai", "113@qq.com");
console.log(user.say());
console.log(User.nation);
// extends继承
class Child extends User {
  constructor(uname, email, sex) {
    // super 调用父类成员
    super(uname, email);
    this.sex = sex;
  }
  say() {
    return `${super.say()},(${this.sex})`;
  }
}
const child = new Child("sushi", "567@qq.com", "man");
console.log(child.say());

2.字符串常用API

let str = "I Love My Country";
// 1. length 属性
console.log("length = ", str.length);
// 2. charAt(), 索引 -> 成员
console.log(str[5]);
// 3. indexOf(): 成员 -> 索引
console.log(str.indexOf("y"));
// 4. replace()替换
console.log(str);
console.log(str.replace("Country", "Mother"));
// 5. substring() ,必须去掉(忽略)结束索引
console.log(str.substring(2, 6));
// 6. split: 字符串 -> 数组
console.log(str.split(""));
// 7. 大小写
console.log(str.toLowerCase());
console.log(str.toUpperCase());

3.数组常用API

//...rest 压缩与展开
arr = [1, 2, 3];
let arr1 = [...arr];
console.log(arr1);
arr = [...arr, 4, 5, 6];
console.log(arr);
// Array.of 打包
let items = [1, 2, 3, 4, 5, 6];
console.log(Array.of(...items));
// Array.from() 类数组 -> 真正的数组
const likeArr = {
  0: "red",
  1: "blue",
  2: "green",
  length: 3,
};
const data = Array.from(likeArr);
console.log(Array.isArray(data) ? "Array" : "no Array");
for (let item of data) {
  console.log(item);
}
let arr2 = [];
// push 尾部插入
console.log(arr2.push(10));
console.log(arr2);
console.log(arr2.push(20, 30));
console.log(arr2);
// pop 尾部弹出
console.log(arr2.pop());
console.log(arr2.pop());
console.log(arr2);
// unshift  头部添加
console.log(arr2.unshift(10));
console.log(arr2);
console.log(arr2.unshift(20, 30, 40));
console.log(arr2);
// shift 头部弹出
console.log(arr2.shift());
console.log(arr2.shift());
console.log(arr2);
// delete
delete arr2[0];
console.log(arr2);