promise与async、await

promise用法

1. promise基本用法

let p1 = new Promise((resolve, reject) => {
	setTimeout(() => {
		resolve('p1-ok');
	}, 1000);
});

let p2 = Promise.resolve('p2-ok');

p1.then((res) => {
	console.log(res);// p1-ok
	return p2;
}).then((res) => {
	console.log(res);// p2-ok
	// ...
});
           

1. Promise.all(Array[Promise] array, Function callback)

   只有当数组里所有的promise实例执行成功,才会变为成功状态,成功回调函数的参数是所有传入的promise的返回值组成的数组

let p1 = new Promise((resolve, reject) => {
	setTimeout(() => {
		resolve('p1-ok');
	}, 1000);
});

let p2 = Promise.resolve('p2-ok');

let p3 = Promise.reject(new Error('出错了!'));

let pAll = Promise.all([p1, p2, p3]);
pAll.then(res => {
	console.log('全部执行成功', res);
}).catch(err => {
	console.log('报错:' + err.message);// 报错:出错了!
}).finally(() => {
	console.log('Promise.all执行完毕');// Promise.all执行完毕
});
           

1. Promise.race(Array[Promise] array, Function callback)

   只要数组中有一个成功,就整个执行成功,成功回调函数的参数为最先执行成功的promise实例的返回值

// ...
let pRace = Promise.race([p1, p2, p3]);
pRace.then(res => {
	console.log('至少一个执行成功', res);// 至少一个执行成功 p2-ok
});
           

async、await

async、await是generator函数的语法糖,是解决回调地狱的最新语法

async function demo() {
	let p1 = new Promise((resolve, reject) => {
		setTimeout(() => {
			resolve('p1-ok');
		}, 1000);
	});
	
	let p2 = Promise.resolve('p2-ok');
	
	let p3 = Promise.reject(new Error('出错了!'));

	try {
		let resAll = await Promise.all([p1, p2, p3]);
		console.log('resAll', resAll);
	} catch(err) {
		console.log('err', err.message);
	}
	
	let res = await Promise.race([p1, p2, p3]);
	console.log('race', res);
}

demo();