promise 异步函数

// promise
let promise = new Prommise((resolve, reject) => {
	setTimeout(() => {
		if (true) {
			resolve({ name: "狗" });
		} else {
			reject("失败了");
		}
	});
}, 2000);

//promise.then(onCompleted, onRejected);
    //onCompleted必需。承诺成功完成时要运行的履行处理程序函数。
    //onRejected可选。承诺被拒绝时要运行的错误处理程序函数

promise.then(result => console.log(result));

//.catch的作用是捕捉前一个函数的错误

promise.catch(error => console.log(error));

promise.then(result => console.log(result))   //{ name: "狗" }
       .catch(error => console.log(error))      //失败了

//async 返回的是一个promise对象

const fn = async() =>{}
async function fn(){}

//(“util”).promisify(包装方法成为promise对象)