const obj = { foo: 'bar', baz: 42 };
console.log(Object.entries(obj)); // [ ['foo', 'bar'], ['baz', 42] ]

const obj = { a: 5, b: 7, c: 9 };
for (const [key, value] of Object.entries(obj)) {console.log(`${key} ${value}`); // "a 5", "b 7", "c 9"
}
Object.entries(obj).forEach(([key, value]) => {console.log(`${key} ${value}`); // "a 5", "b 7", "c 9"
});

const obj = { foo: 'bar', baz: 42 };
const a = Object.entries(obj);
var b= new Map(a)
// {"foo" => "bar", "baz" => 42}

'5'.padStart(10) // '          5'
'5'.padStart(10, '=*') //'=*=*=*=*=5'
'5'.padEnd(10) // '5         '
'5'.padEnd(10, '=*') //'5=*=*=*=*='

//ES2017
//如果你有一个不同长度的项目列表，并希望格式化它们的显示目的，你可以使用padStart
const formatted = [0, 1, 12, 123, 1234, 12345].map(num => num.toString().padStart(10, '0') // 添加 0 直到长度为 10
);
console.log(formatted);
//打印
// [
//     '0000000000',
//     '0000000001',
//     '0000000012',
//     '0000000123',
//     '0000001234',
//     '0000012345',
// ]    

const cars = {'?BMW': '10','?Tesla': '5','?Lamborghini': '0'
}
Object.entries(cars).map(([name, count]) => {//padEnd appends ' -' until the name becomes 20 characters//padStart prepends '0' until the count becomes 3 characters.console.log(`${name.padEnd(20, ' -')} Count: ${count.padStart(3, '0')}`)
});
//打印结果..
// ?BMW - - - - - - -  Count: 010
// ?Tesla - - - - - -  Count: 005
// ?Lamborghini - - -  Count: 000

'heart'.padStart(10, "❤️");
22:10:05.595 "❤️❤️❤heart"

var Car = {name: 'BMW',price: 1000000,set discount(x) {this.d = x;},get discount() {return this.d;},
};
//使用Object.defineProperties将Car的属性复制到ElectricCar2
//并使用Object.getOwnPropertyDescriptors提取Car的属性
const ElectricCar2 = Object.defineProperties({}, Object.getOwnPropertyDescriptors(Car));
//打印ElectricCar2对象“discount”属性的详细信息
console.log(Object.getOwnPropertyDescriptor(ElectricCar2, 'discount'));
//prints..
// { get: [Function: get],
//   set: [Function: set],
//   enumerable: true,
//   configurable: true
// }
// 请注意，getter和setter存在于ElectricCar2对象中，用于'discount'属性！

//ES2015 Promise
function getAmount(userId) {getUser(userId).then(getBankBalance).then(amount => {console.log(amount);});
}****************************//ES2017
async function getAmount2(userId) {var user = await getUser(userId);var amount = await getBankBalance(user);console.log(amount);
}
function getUser(userId) {return new Promise(resolve => {setTimeout(() => {resolve('john')}, 1000)});
}
function getBankBalance(user) {return new Promise((resolve, reject) => {setTimeout(() => {if(user == 'john') {resolve('$1,000');} else {reject(unknown user);}}, 1000)});
}

/异步函数本身返回一个Promise
async function doubleAndAdd(a, b) {a = await doubleAfterlSec(a);b = await doubleAfterlSec(b);return a + b;
}
//用法
doubleAndAdd(1, 2).then(console.log);
function doubleAfterlSec(param) {return new Promise (resolve => {setTimeout(resolve(param * 2), 1000);});
}     

//异步函数本身返回一个Promise
async function doubleAndAdd(a, b) {//注意：这边使用 Promise.all//注意到使用数组解构,捕获结果[a, b] = await Promise.all([doubleAfterlSec(a), doubleAfterlSec(b)]);return a + b;
}
//用法
doubleAndAdd(1, 2).then(console.log);
function doubleAfterlSec(param) {return new Promise (resolve => {setTimeout(resolve(param * 2), 1000);});
}    

// 1. 使用 try catch
async function doubleAndAdd(a, b) {try {a = await doubleAfterlSec(a);b = await doubleAfterlSec(b);} catch (e) {return NaN; // return something
    }return a + b;
}
// 用法
doubleAndAdd('one', 2).then(console.log) //NaN
doubleAndAdd(1, 2).then(console.log) // 6
function doubleAfterlSec(param) {return new Promise((resolve, reject) => {setTimeout(function() {let val = param * 2;isNaN(val) ? reject(NaN) : resolve(val);}, 1000);});
}

//因为异步/等待返回一个Promise，我们可以捕捉整个函数的错误
async function doubleAndAdd(a, b) {a = await doubleAfter1Sec(a);b = await doubleAfter1Sec(b);return a + b;
}
//用法
doubleAndAdd('one', 2)
.then(console.log)
.catch(console.log); //use "catch"
function doubleAfter1Sec(param) {return new Promise((resolve, reject) => {setTimeout(function() {let val = param * 2;isNaN(val) ? reject(NaN) : resolve(val);}, 1000);});
}