promise学习 

const fs = require('fs');
const path = require('path');

fs.readFile(path.join(__dirname, 'data/a.txt'), (err, data)=>{
    console.log(data.toString());
    fs.readFile(path.join(__dirname, 'data/b.txt'), (err, data)=>{
        console.log(data.toString());
        fs.readFile(path.join(__dirname, 'data/c.txt'), (err, data)=>{
            console.log(data.toString());
        });
    });
});
const fs = require('fs');
const path = require('path');

// 1. 创建一个promise （一经创建， 立马执行）链式编程
new Promise((resolve, reject)=>{
    fs.readFile(path.join(__dirname, 'data/a.txt'), (err, data)=>{
        if(err){
            reject(err);
        }
        resolve(data);
    });
}).then((data)=>{
    console.log(data.toString());
    return new Promise((resolve, reject)=>{
        fs.readFile(path.join(__dirname, 'data/b.txt'), (err, data)=>{
            if(err){
                reject(err);
            }
            resolve(data);
        });
    });
}).then((data)=>{
    console.log(data.toString());
    return new Promise((resolve, reject)=>{
        fs.readFile(path.join(__dirname, 'data/c.txt'), (err, data)=>{
            if(err){
                reject(err);
            }
            resolve(data);
        });
    });
}).then((data)=>{
    console.log(data.toString());
}).catch((err)=>{
    console.log(err);
});
 1 const fs = require('fs');
 2 const path = require('path');
 3 
 4 let readFile = (...args) => {
 5     return new Promise((resolve, reject) => {
 6         fs.readFile(...args, (err, data) => {
 7             if (err) {
 8                 reject(err);
 9             }
10             resolve(data);
11         });
12     });
13 };
14 
15 readFile(path.join(__dirname, 'data/c.txt'), 'utf-8')
16     .then((data) => {
17         console.log(data.toString());
18         return readFile(path.join(__dirname, 'data/a.txt'), 'utf-8');
19     }).then((data) => {
20         console.log(data.toString());
21         return readFile(path.join(__dirname, 'data/b.txt'), 'utf-8');
22     }).then((data) => {
23         console.log(data.toString());
24     }).catch((err)=>{
25         console.log(err);
26     });
 1 const fs = require('fs');
 2 const path = require('path');
 3 
 4 let readFile = (...args) => {
 5     return new Promise((resolve, reject) => {
 6         fs.readFile(...args, (err, data) => {
 7             if (err) {
 8                 reject(err);
 9             }
10             resolve(data);
11         });
12     });
13 };
14 
15 Promise.all([
16     readFile(path.join(__dirname, 'data/aa.txt'), 'utf-8'),
17     readFile(path.join(__dirname, 'data/b.txt'), 'utf-8'),
18     readFile(path.join(__dirname, 'data/c.txt'), 'utf-8')
19 ]).then(([data1, data2, data3])=>{
20     console.log({data1, data2, data3});
21 }).catch((err)=>{
22     console.log(err);
23 });

 

posted @ 2019-07-07 18:09  疏影横斜水清浅  阅读(140)  评论(0)    收藏  举报