Use Array.flat instead of array-flatten

[almic]

Depends upon #5595, Adopt Node@18 as minimum supported version.

With this new version, we get Array.flat(depth), which can be used instead of a package. Infinity would have the same behavior as the package, recursively unwrapping nested arrays indefinitely. But, perhaps it might be worth selecting a more reasonable value, to avoid a RangeError, such as when an array contains a reference to itself.

Note

Mimimum Node.js version supported is 11

[wesleytodd]

This is going to fail CI for now, but I figured it was better to approve the CI run for reference. I think this is a good change, but we have a bunch on our plate first so please be patient with us as we get the other things done first.

[admsev]

@gooroodev please take a look

[gooroodev]

Thanks for the alert, @admsev!

1. Summary of Changes

The pull request makes the following changes:

• Replaces the use of the array-flatten library with the native JavaScript Array.prototype.flat method.
• Removes the array-flatten dependency from package.json.
• Updates the code in lib/application.js to use Array.prototype.flat instead of the array-flatten library.

2. Issues, Bugs, and Typos

Issue 1: Incorrect usage of Array.prototype.flat

• Current Code:

  var flatten = Array.prototype.flat;
  var fns = flatten.call(slice.call(arguments, offset), Infinity);
  

  • Problem: The Array.prototype.flat method does not need to be called with call. Instead, it should be used directly on the array.

• Proposed Improvement:

  var fns = slice.call(arguments, offset).flat(Infinity);
  

Issue 2: Redundant variable declaration

• Current Code:

  var flatten = Array.prototype.flat;
  

  • Problem: Declaring flatten is redundant since Array.prototype.flat can be used directly.

• Proposed Improvement: Remove the line:

  var flatten = Array.prototype.flat;
  

3. General Review of Code Quality and Style

Code Quality:

• The code change is straightforward and improves the maintainability by removing an unnecessary dependency.
• The usage of native methods is generally preferred for better performance and reduced dependency overhead.

Code Style:

• The code style remains consistent with the rest of the codebase.
• The changes are minimal and do not introduce any new stylistic issues.

Final Improved Code

Here is the final improved version of the code after addressing the issues:

diff --git a/lib/application.js b/lib/application.js
index 43c9f34b06..ecfe2186db 100644
--- a/lib/application.js
+++ b/lib/application.js
@@ -21,7 +21,6 @@ var http = require('http');
 var compileETag = require('./utils').compileETag;
 var compileQueryParser = require('./utils').compileQueryParser;
 var compileTrust = require('./utils').compileTrust;
-var flatten = require('array-flatten').flatten
 var merge = require('utils-merge');
 var resolve = require('path').resolve;
 var once = require('once')
@@ -34,6 +33,5 @@ var setPrototypeOf = require('setprototypeof')
  */
 
 var slice = Array.prototype.slice;
-var flatten = Array.prototype.flat;
 
 /**
  * Application prototype.
@@ -209,7 +208,7 @@ app.use = function use(fn) {
     }
   }
 
-  var fns = flatten.call(slice.call(arguments, offset), Infinity);
+  var fns = slice.call(arguments, offset).flat(Infinity);
 
   if (fns.length === 0) {
     throw new TypeError('app.use() requires a middleware function')
diff --git a/package.json b/package.json
index d3e2f0a190..5ec37a8f77 100644
--- a/package.json
+++ b/package.json
@@ -29,7 +29,6 @@
   ],
   "dependencies": {
     "accepts": "~1.3.8",
-    "array-flatten": "3.0.0",
     "body-parser": "2.0.0-beta.2",
     "content-disposition": "0.5.4",
     "content-type": "~1.0.4",

This version ensures that Array.prototype.flat is used correctly and removes any redundant variable declarations.

Yours, Gooroo.dev. I'd appreciate it if you could react or reply!

[mmaazahmed]

why is this even a dependency to begin with?

[krzysdz]

why is this even a dependency to begin with?

Array.prototype.flat does not exist in pre-ES2019 ECMAScript standards and Express currently supports old Node.js versions (starting with 0.10), which are way older than this feature.

As for why specifically array-flatten is used, see #2624 and comments in #4707. Basically the idea was to move the util code to separate packages and array-flatten is owned by blakeembrey - an Express.js Technical Committee member.

[mmaazahmed]

Hi Krzysdz Appreciate the response. I was actually referring to having it as a dependency, rather than integrating the functionality directly into the project as a helper function. What were the design considerations of having it as an external dependency whens its only a couple of lines of trivial code. Thanks

[wesleytodd]

Hey @mmaazahmed, can we keep the discussion limited to the changes made in this PR going forward? I am going to hide all our comments here as off topic so that we don't distract the conversation.

[jonchurch]

clopened to rerun CI but forgot 5.0 hasn't dropped the old versions in CI