详解JavaScript中常用操作符的使用

const obj = {
  foo: {
    bar: 123
  }
};

// 普通访问属性的方式
const x = obj.foo.bar; // x = 123

// 使用可选链操作符
const y = obj?.foo?.bar; // y = 123

// 如果对象未定义，则返回 undefined
const z = undefined?.foo?.bar; // z = undefined

const x = undefined ?? 'default'; // x = 'default'

const y = null ?? 'default'; // y = 'default'

const z = 'value' ?? 'default'; // z = 'value'

const a = '' ?? 'default'; // a = ''

const b = '' || 'default'; // b = 'default'

const add = (a, b) => a + b;
console.log(add(1, 2)); // 3

const obj = {
  x: 1,
  add(y) {
    return this.x + y;
  },
  double: () => this.x * 2,
};
console.log(obj.add(2)); // 3
console.log(obj.double()); // NaN

const name = "Alice";
const age = 20;
console.log(`My name is ${name}, and I am ${age} years old.`);
// 'My name is Alice, and I am 20 years old.'

const arr1 = [1, 2, 3];
const arr2 = [4, 5, 6];
const arr3 = [...arr1, ...arr2];
console.log(arr3); // [1, 2, 3, 4, 5, 6]

const obj1 = { x: 1, y: 2 };
const obj2 = { z: 3 };
const obj3 = { ...obj1, ...obj2 };
console.log(obj3); // { x: 1, y: 2, z: 3 }

const obj = { prop: "value" };
const propValue = obj.prop || "default";
console.log(propValue); // 'value'

const arr = [];
const firstValue = arr[0] && arr[0].prop;
console.log(firstValue); // undefined

const age = 20;
const message = age >= 18 ? "You are an adult" : "You are not an adult";
console.log(message); // 'You are an adult'

let count = 0;
count++;
console.log(count); // 1

let num = 5;
const result = --num;
console.log(result); // 4

let count = 0;
count += 1;
console.log(count); // 1

let num = 5;
num *= 2;
console.log(num); // 10

const x = "hello";
console.log(!!x); // true

const y = 0;
console.log(!!y); // false

interface Person {
  name: string;
  age?: number;
}

const person1: Person = { name: "Alice" };
const person2: Person = { name: "Bob", age: 20 };

console.log(1 + "2"); // '12'
console.log(true + true); // 2
console.log("10" - 5); // 5

console.log("100" == 100); // true
console.log("0e1" == 0); // true
console.log("0e0" == 0); // true