Question

在这个应用程序中，我想维护一个日志文件。执行时可能会抛出一些异常。如果有异常，我也想记录它。但实际发生的是在将消息记录到日志文件之前终止应用程序。我尝试仅对log()方法使用promise，它没有修复订单。我该如何解决这个问题？如果我使用promises，我是否必须在每种方法中使用promises（或在每种方法中返回新的promise）？或者还有其他更好的解决方案吗？ createWriteStream.write()是asynchronous函数吗？如果这是为什么它有回电？

//this is my object
var fileHandler = function () {};

//this log everything into a log file
fileHandler.prototype.log = function (logContent) {
    var logWriter = FS.createWriteStream(logFilePath, {
        flags: 'w',
        defaultEncoding: 'utf8',
        autoClose: true
    });
    console.log(logContent);
    logWriter.write(logContent+'\n');

/*
promise.resolve()
.then(function () {
   var logWriter = FS.createWriteStream(logFilePath, {
            flags: 'w',
            defaultEncoding: 'utf8',
            autoClose: true
        });
   console.log(logContent);
})
.then(function () {
   logWriter.write(logContent+'\n');
})
*/


};


//Expedted result:
//if "isTrue" == false, 
//01.this.log() should write the message to file
//02.after that print "test" in console
//03.and then terminate the application with an exception

//But the actual result:
//when i debug        
//logWriter.write(logContent+'\n'); is executed 
//but doesn't log the message before an exceptions is thrown.
fileHandler.prototype.createItem = function (isTrue) {

  if(isTrue){
    this.log('it\'s true');
  }
  else{
    this.log('newException : it\'s not true');
    throw new this.setUserException('newException', 'it\'s not true');
  }
};


//create new instance
var projectModule = new fileHandler();

//add cteate method to projectModule object
projectModule.create = function (isTrue) {
  this.createItem(isTrue);
};

//call create function
projectModule.create(false);

为什么某些同步功能以异常顺序执行

0 个答案: