Determine if a path is subdirectory of another in Node.js

Question

I am working on a MQTT handler for which I want to emit an event for each parent directory where there is a event listener. For example:

If there are the following MQTT paths available, where there are subscriptors –there are event listeners for these paths–

• test
• replyer/request
• test/replyer/request

And someone publishes on topic test/replyer/request/@issuer, there should be 2 events emmited: test, test/replyer/request.

Given than any path is possible and there is no list of available valid events, we must check only if a path is a parent of another. Can we do this with regex? If so, how would it look like? Is there a simpler/more efficient solution?

Answer 1

Let Node itself do the work.

const path = require('path'); const relative = path.relative(parent, dir); return relative && !relative.startsWith('..') && !path.isAbsolute(relative); 

It does normalisation for you as well.

const path = require('path');  const tests = [   ['/foo', '/foo'],   ['/foo', '/bar'],   ['/foo', '/foobar'],   ['/foo', '/foo/bar'],   ['/foo', '/foo/../bar'],   ['/foo', '/foo/./bar'],   ['/bar/../foo', '/foo/bar'],   ['/foo', './bar'],   ['C:\\Foo', 'C:\\Foo\\Bar'],   ['C:\\Foo', 'C:\\Bar'],   ['C:\\Foo', 'D:\\Foo\\Bar'], ];  tests.forEach(([parent, dir]) => {     const relative = path.relative(parent, dir);     const isSubdir = relative && !relative.startsWith('..') && !path.isAbsolute(relative);     console.log(`[${parent}, ${dir}] => ${isSubdir} (${relative})`); }); 

Works on Windows across drives too.

[/foo, /foo] => false () [/foo, /bar] => false (..\bar) [/foo, /foobar] => false (..\foobar) [/foo, /foo/bar] => true (bar) [/foo, /foo/../bar] => false (..\bar) [/foo, /foo/./bar] => true (bar) [/bar/../foo, /foo/bar] => true (bar) [/foo, ./bar] => false (..\Users\kozhevnikov\Desktop\bar) [C:\Foo, C:\Foo\Bar] => true (Bar) [C:\Foo, C:\Bar] => false (..\Bar) [C:\Foo, D:\Foo\Bar] => false (D:\Foo\Bar)