如何在NodeJs中读取文件到变量？

i'm pretty new into NodeJs. And i am trying to read a file into a variable. Here is my code.

我是NodeJs的新手。我试图将文件读入变量。这是我的代码。

var fs = require("fs"),
    path = require("path"),
    util = require("util");
        var content;
        console.log(content);
        fs.readFile(path.join(__dirname,"helpers","test.txt"), 'utf8',function (err,data) {
            if (err) {
                console.log(err);
                process.exit(1);
            }
            content = util.format(data,"test","test","test");
        });
        console.log(content);

But every time i run the script i get undefined and undefined

但每次我运行脚本我都会得到未定义和未定义

What am i missing? Help please!

我错过了什么？请帮助！

1 个解决方案

#1

As stated in the comments under your question, node is asynchronous - meaning that your function has not completed execution when your second console.log function is called.

正如您的问题中的注释所述，节点是异步的 - 这意味着在调用第二个console.log函数时，您的函数尚未完成执行。

If you move the log statement inside the the callback after reading the file, you should see the contents outputted:

如果在读取文件后在回调内移动log语句，则应该看到输出的内容：

var fs = require("fs"),
    path = require("path"),
    util = require("util");
        var content;
        console.log(content);
        fs.readFile(path.join(__dirname,"helpers","test.txt"), 'utf8',function (err,data) {
            if (err) {
                console.log(err);
                process.exit(1);
            }
            content = util.format(data,"test","test","test");
            console.log(content);
        });

Even though this will solve your immediately problem, without an understanding of the async nature of node, you're going to encounter a lot of issues.

即使这将解决您的问题，如果不了解节点的异步性质，您将遇到很多问题。

This similar * answer goes into more details of what other alternatives are available.

这个类似的*答案详细介绍了其他替代方案的可用性。

#1