blocks|key|4457750|text|将数据插入到文本文件的中间并不是一项简单的任务。如果可能，您应该将其附加到文件的末尾。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|4457751|将数据附加到某个文本文件最简单的方法是使用fs+module的内置fs.appendFile(filename,+data[,+options],+callback)+function|offset|length|style|CODE|4457752|var+fs+=+require('fs')
fs.appendFile('log.txt',+'new+data',+function+(err)+{
++if+(err)+{
++++//+append+failed
++}+else+{
++++//+done
++}
})|code-block|syntax|javascript|4457753|但是，如果您想多次将数据写入日志文件，那么最好使用fs.createWriteStream(path[,+options])+function：|4457754|var+fs+=+require('fs')
var+logger+=+fs.createWriteStream('log.txt',+{
++flags:+'a'+//+'a'+means+appending+(old+data+will+be+preserved)
})

logger.write('some+data')+//+append+string+to+your+file
logger.write('more+data')+//+again
logger.write('and+more')+//+again|4457755|节点将在您每次调用.write时将新数据追加到文件中，直到您关闭应用程序或手动关闭调用.end的流|4457756|logger.end()+//+close+string|4457757|entityMap|0|LINK|mutability|MUTABLE|url|https://nodejs.org/api/fs.html|1|https://nodejs.org/api/fs.html#fs_fs_appendfile_filename_data_options_callback|2|https://nodejs.org/api/fs.html#fs_fs_createwritestream_path_options^0|0|L|2|X|1E|L|9|0|X|1N|1|0|0|P|11|P|1A|2|0|0|9|6|17|4|0|0^^$0|@$1|2|3|4|5|6|7|16|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|17|8|@$D|18|E|19|F|G]|$D|1A|E|1B|F|G]]|9|@$D|1C|E|1D|1|1E]|$D|1F|E|1G|1|1H]]|A|$]]|$1|H|3|I|5|J|7|1I|8|@]|9|@]|A|$K|L]]|$1|M|3|N|5|6|7|1J|8|@$D|1K|E|1L|F|G]]|9|@$D|1M|E|1N|1|1O]]|A|$]]|$1|O|3|P|5|J|7|1P|8|@]|9|@]|A|$K|L]]|$1|Q|3|R|5|6|7|1Q|8|@$D|1R|E|1S|F|G]|$D|1T|E|1U|F|G]]|9|@]|A|$]]|$1|S|3|T|5|J|7|1V|8|@]|9|@]|A|$K|L]]|$1|U|3|-4|5|6|7|1W|8|@]|9|@]|A|$]]]|V|$W|$5|X|Y|Z|A|$10|11]]|12|$5|X|Y|Z|A|$10|13]]|14|$5|X|Y|Z|A|$10|15]]]]

Inserting data into the middle of a text file is not a simple task. If possible, you should append it to the end of your file.

The easiest way to append data some text file is to use build-in <a href="https://nodejs.org/api/fs.html#fs_fs_appendfile_filename_data_options_callback" rel="noreferrer"><code>fs.appendFile(filename, data[, options], callback)</code> function</a> from <a href="https://nodejs.org/api/fs.html" rel="noreferrer"><code>fs</code> module</a>:

<pre><code>var fs = require('fs')
fs.appendFile('log.txt', 'new data', function (err) {
 if (err) {
 // append failed
 } else {
 // done
 }
})
</code></pre>

But if you want to write data to log file several times, then it'll be best to use <a href="https://nodejs.org/api/fs.html#fs_fs_createwritestream_path_options" rel="noreferrer"><code>fs.createWriteStream(path[, options])</code> function</a> instead:

<pre><code>var fs = require('fs')
var logger = fs.createWriteStream('log.txt', {
 flags: 'a' // 'a' means appending (old data will be preserved)
})

logger.write('some data') // append string to your file
logger.write('more data') // again
logger.write('and more') // again
</code></pre>

Node will keep appending new data to your file every time you'll call <code>.write</code>, until your application will be closed, or until you'll manually close the stream calling <code>.end</code>:

<pre><code>logger.end() // close string
</code></pre>

blocks|key|4457780|text|只需使用fs模块和类似以下内容：|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|4457781|fs.appendFile('server.log',+'string+to+append',+function+(err)+{
+++if+(err)+return+console.log(err);
+++console.log('Appended!');
});|code-block|syntax|javascript|4457782|entityMap^0|4|2|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@$9|N|A|O|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|P|8|@]|D|@]|E|$I|J]]|$1|K|3|-4|5|6|7|Q|8|@]|D|@]|E|$]]]|L|$]]

Simply use <code>fs</code> module and something like this:

<pre><code>fs.appendFile('server.log', 'string to append', function (err) {
 if (err) return console.log(err);
 console.log('Appended!');
});
</code></pre>

blocks|key|4457812|text|我创建了一个日志文件，使用"Winston“记录器将数据打印到文本文件中。源代码在下面，|type|unstyled|depth|inlineStyleRanges|entityRanges|data|4457813|const+{+createLogger,+format,+transports+}+=+require('winston');
var+fs+=+require('fs')
var+logger+=+fs.createWriteStream('Data+Log.txt',+{
++flags:+'a'+
})
const+os+=+require('os');
var+sleep+=+require('system-sleep');
var+endOfLine+=+require('os').EOL;
var+t+=+'+++++++++++++';
var+s+=+'+++++++++';
var+q+=+'+++++++++++++++';
var+array1=[];
var+array2=[];
var+array3=[];
var+array4=[];
++++++++++++++
array1[0]++=++78;
array1[1]++=++56;
array1[2]++=++24;
array1[3]++=++34;
++++++++++++++++++
for+(var+n=0;n<4;n%2B%2B)
{
++array2[n]=array1[n].toString();
}
+++++++++++++++++
for+(var+k=0;k<4;k%2B%2B)
{
++array3[k]=Buffer.from('++++++++++++++++++++');
}

for+(var+a=0;a<4;a%2B%2B)++
{
++array4[a]=Buffer.from(array2[a]);
}

for+(m=0;m<4;m%2B%2B)
{
++array4[m].copy(array3[m],0);
}

logger.write('Date'%2Bq);
logger.write('Time'%2B(q%2B'++'))
logger.write('Data+01'%2Bt);
logger.write('Data+02'%2Bt);+
logger.write('Data+03'%2Bt);
logger.write('Data+04'%2Bt)

logger.write(endOfLine);
logger.write(endOfLine);

function+mydata()++++++//user+defined+function
{
++logger.write(datechar%2Bs);
++logger.write(timechar%2Bs);
++for+(+n+=+0;+n+<+4;+n%2B%2B)+
++{
+++logger.write(array3[n]);
++}
++logger.write(endOfLine);+
}

var+now+=+new+Date();
var+dateFormat+=+require('dateformat');
var+date+=+dateFormat(now,"isoDate");
var+time+=+dateFormat(now,+"h:MM:ss+TT+");
var+datechar+=+date.toString();
var+timechar+=+time.toString();
mydata();
sleep(5*1000);|code-block|syntax|javascript|4457814|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

I created a log file which prints data into text file using &quot;Winston&quot; logger. The source code is here below,
<pre><code>const { createLogger, format, transports } = require('winston');
var fs = require('fs')
var logger = fs.createWriteStream('Data Log.txt', {
 flags: 'a' 
})
const os = require('os');
var sleep = require('system-sleep');
var endOfLine = require('os').EOL;
var t = ' ';
var s = ' ';
var q = ' ';
var array1=[];
var array2=[];
var array3=[];
var array4=[];
 
array1[0] = 78;
array1[1] = 56;
array1[2] = 24;
array1[3] = 34;
 
for (var n=0;n&lt;4;n++)
{
 array2[n]=array1[n].toString();
}
 
for (var k=0;k&lt;4;k++)
{
 array3[k]=Buffer.from(' ');
}

for (var a=0;a&lt;4;a++) 
{
 array4[a]=Buffer.from(array2[a]);
}

for (m=0;m&lt;4;m++)
{
 array4[m].copy(array3[m],0);
}

logger.write('Date'+q);
logger.write('Time'+(q+' '))
logger.write('Data 01'+t);
logger.write('Data 02'+t); 
logger.write('Data 03'+t);
logger.write('Data 04'+t)

logger.write(endOfLine);
logger.write(endOfLine);

function mydata() //user defined function
{
 logger.write(datechar+s);
 logger.write(timechar+s);
 for ( n = 0; n &lt; 4; n++) 
 {
 logger.write(array3[n]);
 }
 logger.write(endOfLine); 
}

var now = new Date();
var dateFormat = require('dateformat');
var date = dateFormat(now,&quot;isoDate&quot;);
var time = dateFormat(now, &quot;h:MM:ss TT &quot;);
var datechar = date.toString();
var timechar = time.toString();
mydata();
sleep(5*1000);
</code></pre>

I want to create a simple Log System, which prints a line before the past line into a txt file by using Node.js, but i dont know how the File System from Node.js works. Can someone explain it ?

Node.js Write a line into a .txt file

日志文件

文件系统

我想创建一个简单的日志系统，它使用Node.js将上一行之前的一行打印到txt文件中，但我不知道Node.js的文件系统是如何工作的。有人能解释一下吗？

问Node.js在.txt文件中写入一行
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