How to solve nodejs path problem

This article mainly introduces the solution to the path problem of nodejs. The content is quite good. I will share it with you now and give it as a reference.

A recent development project of the company used nodejs as the backend. In the past two days, I needed to package it for customer demonstration, so I asked a guy from the company to transplant the packaging tool from the previous 3D computer room. After packaging, I found that the project that originally ran well in the development environment could no longer be accessed. There is a problem that the homepage of the project cannot be accessed:

can not get file index.html

express.static

What’s the problem?

The nodejs backend uses express, and index.html is a static file. We know that static files, such as images, CSS, JavaScript files, etc., can be easily hosted through Express's built-in express.static.

Pass the directory where the static resource files are located as a parameter to express.static middleware to provide access to static resource files. For example, assuming that images, CSS and JavaScript files are placed in the public directory, you can use the following code:

app.use(express.static('public'));

So, find the code in the project and check where the static call is, which is very similar to the above line of code:

app.use(express.static('public'));

At this point, I have discovered the problem. I told my friends that this problem can be solved without using relative paths. Due to the packaging time limit, I asked my friends to deal with it briefly first. After packaging, I will sort out my thoughts:

app.use(express.static('resource/public'));

Of course, the most important thing is that this problem is not difficult. If you study more, it will be very easy. If the problem is easy to find, this problem will not occur, so friends, please do it yourself.

Well, you read that right, this place is still a relative directory. It will be changed to a better situation in subsequent products.

express.static method analysis

In fact, if the express.static method passes in a relative path, express will convert it by itself For an absolute path, we can check the source code and find the following code in express.js:

exports.static = require('serve-static');

Description static calls the serve-static package, find this package directly, check index.js, you can see the code , Listed below are two important lines

...
var resolve = require('path').resolve
...
opts.root = resolve(root)
...

These two lines are the code for express to convert a relative directory into an absolute directory. It can be seen that the resolve method of the built-in object path is ultimately used. Continue reading. .

resolve method of path object

Directly view the api document of this method, as follows: https://nodejs.org/api/path .html#path_path_resolve_paths

The following is an explanation of this method:

The path.resolve() method resolves a sequence of paths or path segments into an absolute path.

What does it mean? This method organizes a series of paths or path segments into an absolute path, such as

path.resolve('/foo','bar');
// return /foo/bar

Please refer to the documentation for detailed instructions. There is a sentence here that requires special attention:

If after processing all given path segments an absolute path has not yet been generated, the current working directory is used.

What does it mean, that is, if all path segments have been processed , and does not generate an absolute path, the current working directory must be used. For example:

path.resolve('bar');
// 加上 /Users/terry 是当前工作目录， return /Users/terry/bar

A more complex example in the api document (note here when resolving, from right to left, refer to the document for details):

path.resolve('wwwroot', 'static_files/png/', '../gif/image.gif');
// if the current working directory is /home/myself/node,
// this returns '/home/myself/node/wwwroot/static_files/gif/image.gif'

The question now is, what is Current working directory.

nodejs current working directory current working directory

nodejs The current working directory is the directory where Node is started. In other words, whichever directory you enter from to start node will return to that directory.

Note that this directory does not refer to the directory where the js file is located

The current working directory can be obtained through the process.cwd() method.

The following is an example to introduce the current working directory. If you write a js file, test.js, in the /Users/terry/Documents/JSWorkspace directory, there is only one line of code:

console.log(process.cwd());

At this time, if you execute the command under the directory /Users/terry/Documents/JSWorkspace: node test.js, the output is as follows:

/Users/terry/Documents/JSWorkspace

But if you execute the command under the directory /Users/terry/Documents/: node ./JSWorkspace/test.js, the output result is:

/Users/terry/Documents

So you can see in which directory you execute the node command, and the current directory is that directory.

Returning to the previous packaging issue, since during the development stage, the node command is generally executed directly in the directory where the js file is located, so there is no problem in writing the relative directory relative to the directory of the current js file. .

But after packaging, the execution of node is placed in the upper layer of the js directory. At this time, the relative directory "public" is no longer relative to the js file, but relative to the previous layer. Naturally, this folder cannot be found, and therefore the index.html file under the folder cannot be found. .

How to solve

Solution:

1.在前面已经说过了，改这个相对目录。但这种方法很蹩脚。因为，启动node命令的目录可能会变；而是如果这应该，开发阶段的node命令执行也需要跟着改。 总之不是兼容性很好的方法。

2.直接使用绝对路径。 但是这个绝对路径在不同的机器上又不一样，该如何解决呢？可以考虑使用全局变量__dirname.

全局变量__dirname

查看api文档 https://nodejs.org/api/modules.html#modules_dirname

看到解释如下：

The directory name of the current module. This is the same as the path.dirname() of the __filename。

啥意思呢，及时返回nodejs 的js文件的所在目录。

有了这个变量之后，我们就可以用如下代码解决这个问题。

app.use(express.static(__dirname + '/public'));

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