Question

我有一个长度为X的文件，它被一个长度为X-Y的字符串覆盖。问题是，文件仍然保留超过X-Y的信息，因此它与第一个较长的文件一样长。所以这是我的测试输出，让我适合：

文件起始时间为：

{
    "sOption1": "String",
    "nOption2": 23.5,
    "sOption3": "String",
    "bOption3B": true,
    "anOption4": [
        5,
        6,
        7
    ],
    "sNewString": "FruitSalad",
    "bNewBoolean": false,
    "iNewNumber": 14.2,
    "anNewArray": [
        1,
        2,
        3,
        4,
        5,
        6,
        7,
        8,
        9,
        10
    ],
    "oNewObject": {
        "bToBeOrNotToBe": true,
        "sFinishQuote": "That is the question"
    }
}

将正在写入的数据更改为以下内容：

{
    "sOption1": "String",
    "nOption2": 23.5,
    "sOption3": "String",
    "bOption3B": true,
    "anOption4": [
        5,
        6,
        7
    ],
    "sNewString": "YummyYummy",
    "bNewBoolean": true,
    "iNewNumber": 2.14,
    "anNewArray": [
        10,
        9
    ],
    "oNewObject": {
        "bToBeOrNotToBe": false,
        "sNewQuote": "To die, to sleep, no more"
    }
}

此后，文件现在是：

{
    "sOption1": "String",
    "nOption2": 23.5,
    "sOption3": "String",
    "bOption3B": true,
    "anOption4": [
        5,
        6,
        7
    ],
    "sNewString": "YummyYummy",
    "bNewBoolean": true,
    "iNewNumber": 2.14,
    "anNewArray": [
        10,
        9
    ],
    "oNewObject": {
        "bToBeOrNotToBe": false,
        "sNewQuote": "To die, to sleep, no more"
    }
}       "bToBeOrNotToBe": true,
        "sFinishQuote": "That is the question"
    }
}}

看到对象末尾的垃圾？它是从前一个文件遗留下来的，即使我用以下代码写出来：

DeviceConfiguration.prototype.SetPersistentUserOption = function(sNewOptionName, NewOption)
{
    var sNewFile = "";
    var fs = require('fs');

    //if one of the primitive types, it's simple, just add it to object
    if(typeof(NewOption) == "string" || typeof(NewOption) == "number" || typeof(NewOption) == "boolean")
    {
        this.oPersistentUserOptions[sNewOptionName] = NewOption;
    }
    else if(NewOption instanceof Array)
    {
        //blank out array if it was there already
        this.oPersistentUserOptions[sNewOptionName] = [];   

        //now go back and copy each element over one at a time
        for(var nIndex = 0; nIndex < NewOption.length; nIndex++)
        {   this.oPersistentUserOptions[sNewOptionName][nIndex] = NewOption[nIndex];    }
    }
    else if(NewOption instanceof Object)
    {
        //blank out object if it was there already
        this.oPersistentUserOptions[sNewOptionName] = {};   

        //now go back and copy each element over one at a time
        for(Member in NewOption)
        {   this.oPersistentUserOptions[sNewOptionName][Member] = NewOption[Member];    
        }
    }

    //stringify the object, and make it pretty with options null, 4
    sNewFile = JSON.stringify(this.oPersistentUserOptions, null, 4);

    //write to the file, parameter is immediately in object memory though
    fs.writeFile(PERSISTENT_USER_SELECTED_OPTIONS_FILENAME, sNewFile, function(err){console.log(err);});
    //fs.writeFileSync(PERSISTENT_USER_SELECTED_OPTIONS_FILENAME, sNewFile);

    console.log(sNewFile.length);
    console.log(sNewFile);
};

我已经检查过以确保sNewFile变量的长度正确，而且确实如此。在后续写入磁盘之间我也暂停了6秒钟，所以我看不出这可能是一个时间问题。

如果我使用writeFileSync，问题就会消失，但我真的没有为这个应用程序做同步写操作的选项，因为我对时序要求很高，并且不想放慢写入磁盘的速度。

我在node.js 0.8.21上，但它看起来并不像fs和最新版本之间的fs一样。

有人打过这样的东西吗？这给了我适合。。。

Answer 1

我刚刚在0.8.21（linux）上对此进行了测试，这可以按预期工作。

var fs = require('fs')

var str1 = "aaaaaaaaaa"
var str2 = "bbbbbb"
var str3 = "bbbbbbaaaa"

fs.writeFile('test',str1,function(){
  fs.writeFile('test',str2,function(){
    fs.readFile('test','utf8',function(err,buff){
      console.log(buff === str2)
      console.log(buff === str3)
    })
  })
})

output
> node test.js
true
false

node.js fs.writeFile未完全覆盖文件

1 个答案: