text.js

//1.变量&数据类型
const userName = "chenZhenLi";//字符串
const age = 23; //数字
const isStudent = true;//布尔类型
console.log(userName);
console.log(age);
console.log(isStudent);

let a = 123//数字
let b = "hello"//string
let c = true//布尔
let d//undefined
let e = null//object
console.log(typeof(a));
console.log(typeof(b));
console.log(typeof(c));
console.log(typeof(d));
console.log(typeof(e));
//为什么null 是object？

//2.运算符 & 条件判断
console.log(10 + 5);//预期15
console.log("10" + 5);//105
console.log("10" - 5);//5

let score = 90;
if (score >= 90){
    console.log("优秀");
} else if (score < 90 && score >= 60){
    console.log("及格");
} else {
    console.log("不及格");
}

//三元运算符，好像只适合一选二的部分
let finalResult = score >= 60 ? console.log("pass"): console.log("fail");



const array1 = [1, 2, 3, 4, 5]
const array2 = array1.pop();
console.log(array2.length);
//如何使用length打印数组长度？？

const person = {
    name: "Chenzhenli",
    age: 23,
    gender: "female"
}

console.log(person.name)
person.age = 17;
console.log(person.age);
//如何给对象增加属性hobby
person.hobby = " reading";
person["hometown"] = "Wuxi";
person.member = true;
console.log(person);


function introduce(person){
    return `Hello,my name is ${person.name},I'm ${person.age} years old.`;
}
let message = introduce(person);
console.log(message);
 

const multiply = (a,b) => a + b ;
let result = multiply(3,5);
console.log(result);

function isAdult(x){
    if (x.age >= 18) {
        return true;
    }else {
        return false;
    }
}
const result1 = isAdult(person);
console.log(result1);

function isMember(x){
    if (x.member = true){
        return 80;
    }else {
        return 100;
    }
}

const priceFinal = isMember(person);
console.log(priceFinal);

//数组
const fruits = ["watermelon", "apple","banana"];
//打印第一个元素和最后一个元素
console.log(fruits[0]);
console.log(fruits[fruits.length -1]); 
//使用push添加元素
fruits.push("pear","peach");
fruits.pop();
console.log(fruits.length);

//遍历数组
for (const fruit of fruits) {
    console.log(fruit);
}
//使用forEach遍历数组,有点不太记得了
fruits.forEach(item => console.log(item));

//综合练习
let users = [
  { name: "Tom", age: 17 },
  { name: "Jerry", age: 20 },
  { name: "Lucy", age: 16 }
]
//要求遍历users
users.forEach(item => console.log(item));
//打印年龄大于18岁的用户名字
let userResult = users
    .filter (({ age }) => age >= 18)
    .map(({ name }) => name);

console.log(userResult);

//DOM相关
const btn = document.getElementById('myBtn');

btn.addEventListener('click', () => {
    console.log("按钮被点击了");
})