Javascript 如何在node.js中沿.then链传递承诺数据?
我试图通过Promise链传递readFile的数据 它可以读取,但当我将读取的数据传递给writeFile时,它接收到未定义的数据并写入文件: 以下是输出:Javascript 如何在node.js中沿.then链传递承诺数据?,javascript,node.js,promise,Javascript,Node.js,Promise,我试图通过Promise链传递readFile的数据 它可以读取,但当我将读取的数据传递给writeFile时,它接收到未定义的数据并写入文件: 以下是输出: node promise.js In fileFunction: promiseResolveCallback(): File found! readFromFileCallback: 111111111111111111111111111111111111111111111111111111111111111111111111111
node promise.js
In fileFunction:
promiseResolveCallback(): File found!
readFromFileCallback: 11111111111111111111111111111111111111111111111111111111111111111111111111111111
11111111111111111111111111111111111111111111111111111111111111111111111111111111
writeToFileCallback: undefined
我的代码:
var objFs = require( 'fs' )
function promiseResolveCallback( arg )
{
console.log("promiseResolveCallback(): ", arg)
}
function promiseRejectionCallback( arg )
{
console.log("promiseRejectionCallback(): ", arg)
throw -999;
}
function writeToFileCallback( argPromise )
{
objFs.writeFile( 'new.js',
argPromise.data,
( argError ) =>
{
if( argError )
throw argError
else
console.log( "writeToFileCallback: Written in new.js!" )
}
)
}
function readFromFileCallback()
{
return new Promise( (resolve, reject ) =>
{
objFs.readFile( 'new.js', ( argError, argData ) =>
{
if( argError )
{
reject( argError )
console.log( "readFromFileCallback: " + argError )
}
else
{
resolve( "read file \n")
console.log( "readFromFileCallback: " + argData )
}
}
)
}
)
}
function fileFunction()
{
console.log("In fileFunction:")
return new Promise( ( resolve, reject ) =>
{
objFs.open( 'new.js',
'r',
( argError, argFD ) =>
{
if( argError )
{
reject( new Error("File not found!"), 1000);
}
else
{
resolve("File found!", 1000);
}
}
)
}
);
}
var objPromise = fileFunction()
objPromise.then( promiseResolveCallback, promiseRejectionCallback )
.then( readFromFileCallback )
.then( writeToFileCallback )
objPromise.catch( ( argError ) =>
{
console.error( argError )
}
)
我对承诺这个话题很陌生。但我认为您需要在readFromFileCallback中使用argData进行解析。您可以使用默认情况下提供的fs.Promisesfrom 10.0进行读写。 范例 输出
well done
Put your args data here
fs已经有了承诺的APi。请多读,谢谢。使用wait和async已经解决了这个问题。我希望通过使用just Promissions而不使用Wait async来解决这个问题。这很有帮助。其次,我应该使用argPromise而不是argPromise.data。这也有帮助。非常感谢。
well done
Put your args data here