Everything about path.join vs path.resolve in NodeJS

path is the inbuilt module in NodeJs. It is often used to generate absolute paths for files or resources. join and resolve are the quite commonly and interchangeably used methods of the path module. 

In most of the cases the way join and resolve methods used by us lead to the same result but there's a notable difference between those methods, understanding which can help us to use the path module effectively. 

path.join(__dirname, 'public/logo.png'); // /home/user/project_dir/public/log.png
path.resolve(__dirname, 'public/logo.png'); // /home/user/project_dir/public/log.png

In the above code snippet __dirnname is a global variable that gives the absolute path of your project directory.

console.log(__dirname); // /home/user/project_dir

To quickly get an idea of the difference between path.join and path.resolve, just remove the __dirname from both the methods in the above codes and observe the results.

path.join('public/logo.png'); // public/log.png
path.resolve('public/logo.png'); // /home/user/project_dir/public/log.png

So it should have given some idea of how join and resolve methods are working. Let's dive into more details and differences between these two methods.

Difference between path join vs resolve

Understanding path.join method

join method takes path segments as arguments and joins them together using the platform-specific separator(/ in Linux and \ in Windows) as a delimiter and then normalizes the resulting path.

So path.join simply joins the paths that are given to it. Let's have different scenarios below.

path.join('a', 'b', 'c'); // a/b/c
path.join('a', '/b', 'c'); // a/b/c
path.join('a', 'b', '../c'); // a/c -> normalized
path.join(''); // .
path.join(); // -> No result because zero length path segments are ignored
path.join(__dirname, 'public/logo.png'); // /home/user/project_dir/public/log.png

The path segment for __dirname as seen earlier is /home/user/project_dir so joining that with public/logo.png gives 

/home/user/project_dir/public/log.png

Make a note that path.join takes only valid strings as path segments else it will throw an error.

Now let's understand path.resolve.

Understanding path.resolve method

resolve method takes path segments as arguments just like the join method but it resolves or returns an absolute path always with normalization(which means ../.. such paths get resolved) and that's the main difference between join and resolve.

But few things need to be taken care of to get the correct absolute path from the path.resolve. For instance, the given sequence of paths or path segments are processed from right to left, with each subsequent path prepended until an absolute path is constructed. 

Let's see various path.resolve scenarios to understand it better.

path.resolve('a', 'b', 'c'); // /home/user/project_dir/a/b/c
path.resolve('a', '/b', 'c'); // /b/c -> from right to left until it encounters '/' is considered for absolute path
path.resolve('a', 'b', '../c'); // /home/user/project_dir/a/c -> normalized
path.resolve(''); // /home/user/project_dir/
path.resolve(); // /home/user/project_dir/

Just like path.join, resolve also takes only the valid path segments as arguments else it will throw an error.

So it should be clear by now that join just joins the path segments given as arguments where as resolve joins or resolves the path segments with the absolute path of the root directory or the absolute path that is given as an argument to the path.resolve. 

From this understanding of these methods, we can avoid path.join most of the times to obtain an absolute path using __dirname, because path.resolve actually takes into account the absolute path of the root directory while resolving the path segments.

__dirname === path.resolve() // true

// Instead of this
path.join(__dirname, 'public/logo.png'); // /home/user/project_dir/public/log.png

// You can use this to get the absolute path
path.resolve('public/logo.png'); // /home/user/project_dir/public/log.png

Keep in mind that whenever path.resolve encounters / for the first time from right to left it ends the path until there as the absolute path. 

And that is all about path join vs resolve details. Hope this article has clarified and given you a clear understanding of the differences between these two methods.