Question

这是我的代码：

var fs = require('fs');

var printMsg = function (msg) {
    console.log("printMsg: " + msg)
};

var myWrite = function (filename, content) {
    return new Promise(function (resolve, reject) {
        fs.writeFile(filename, content, function (err) {
            console.log("content: " + content);
            if (err || content.includes('Fail')) {
               console.log("promise rejected for content: '" + content + "'");
               reject("error writing");
            }
            else {
               console.log("promise resolved for content: '" + content + "'");
               resolve("ok");
            }
        });
    });
};

myWrite("test.txt", "Hello world")
    .then(myWrite("test.txt", "Failed"))
    .then(myWrite("test.txt", "How are you?"))
    .catch(printMsg);

在这个例子中，我预计事情将按此顺序发生：

日志将打印内容＆＃34; Hello world＆＃34;
该功能用＆＃34; ok＆＃34;。
日志将打印内容＆＃34;失败＆＃34;
该函数拒绝了它＆＃34;错误写入＆＃34;消息。
将跳过下一个承诺。
catch将执行第二个promise，并显示消息＆＃34;错误写入＆＃34;

实际结果非常令人困惑，所有的promises都是异步的，所有的promises都没有catch函数。

输出：

content: Hello world
promise resolved for content: 'Hello world'
content: How are you?
promise resolved for content: 'How are you?'
content: Failed
promise rejected for content: 'Failed'

输出有时会发生变化，也可能是：

content: How are you?
promise resolved for content: 'How are you?'
content: Hello world
promise resolved for content: 'Hello world'
content: Failed
promise rejected for content: 'Failed'

如果我在＆＃34; writeFile＆＃34;之前移动了内容的日志。函数，它将首先以异步顺序记录所有内容名称，这意味着所有承诺一起执行。有人可以解释一下我做错了什么吗？

感谢＆＃39;！小号

其次，函数在promise中的第一个函数之前运行

0 个答案: