如何在不覆盖文本的情况下在javascript中写入文本文件？

Question

Past research I've done on this topic says that this code:

    const filestream = require('fs');
    for(let a = 0; a < 4; a++) {
        fs.writeFileSync('test.txt', 'test' + a + '\n', 'UTF-8', {'flags': 'a'});
    }

should output

test0
test1
test2
test3

to test.txt. However, all I'm seeing is test3, indicating that each write to the file is overwriting all existing text. Despite my use of the 'a' flag. What's going on here?

Answer 1

我认为您应该为此使用另一个功能，您可以尝试以下操作吗？

fs.appendFileSync('test.txt', 'test' + a + '\n');

Answer 2

fs.writeFileSync() replaces the entire contents of the file with your new content. It does not append content to the end. There are multiple ways to append to the end of a file.

The simplest mechanism is fs.appendFileSync() and that will work for you, but it isn't very efficient to call that in a loop because internally, fs.appendfileSync() will call fs.openSync() , fs.writeSync() and the fs.closeSync() for each time through the loop.

It would be better to open the file once, do all your writing and then close the file.

const fs = require('fs');

const fd = fs.openSync('temp.txt', 'w');
for (let a = 0; a < 4; a++) {
    fs.writeSync(fd, 'test' + a + '\n', 'utf-8');
}
fs.closeSync(fd);

Or, you can collect your data and then write it all at once:

let data = [];
for (let a = 0; a < 4; a++) {
    data.push('test' + a + '\n');
}    
fs.writeFileSync('temp.txt', data.join(''), 'utf-8');