remove array-flatten dependency, no longer necessary

replaced array-flatten dependency with the new flat() method from JavaScript, which is supported in Node.js version 11.0.0 and above. This simplifies the code and reduces the number of dependencies. Proposed change for Express.js v5.

lib/application.js

@@ -25,7 +25,6 @@ var compileETag = require('./utils').compileETag;
 var compileQueryParser = require('./utils').compileQueryParser;
 var compileTrust = require('./utils').compileTrust;
 var deprecate = require('depd')('express');
-var flatten = require('array-flatten');
 var merge = require('utils-merge');
 var resolve = require('path').resolve;
 var setPrototypeOf = require('setprototypeof')
@@ -211,7 +210,7 @@ app.use = function use(fn) {
     }
   }
 
-  var fns = flatten(slice.call(arguments, offset));
+  var fns = slice.call(arguments, offset).flat(Infinity)
 
   if (fns.length === 0) {
     throw new TypeError('app.use() requires a middleware function')

lib/router/index.js

@@ -19,7 +19,6 @@ var methods = require('methods');
 var mixin = require('utils-merge');
 var debug = require('debug')('express:router');
 var deprecate = require('depd')('express');
-var flatten = require('array-flatten');
 var parseUrl = require('parseurl');
 var setPrototypeOf = require('setprototypeof')
 
@@ -456,7 +455,7 @@ proto.use = function use(fn) {
     }
   }
 
-  var callbacks = flatten(slice.call(arguments, offset));
+  var callbacks = slice.call(arguments, offset).flat(Infinity);
 
   if (callbacks.length === 0) {
     throw new TypeError('Router.use() requires a middleware function')

lib/router/route.js

@@ -14,7 +14,6 @@
  */
 
 var debug = require('debug')('express:router:route');
-var flatten = require('array-flatten');
 var Layer = require('./layer');
 var methods = require('methods');
 
@@ -182,7 +181,7 @@ Route.prototype.dispatch = function dispatch(req, res, done) {
  */
 
 Route.prototype.all = function all() {
-  var handles = flatten(slice.call(arguments));
+  var handles = slice.call(arguments).flat(Infinity);
 
   for (var i = 0; i < handles.length; i++) {
     var handle = handles[i];
@@ -205,7 +204,7 @@ Route.prototype.all = function all() {
 
 methods.forEach(function(method){
   Route.prototype[method] = function(){
-    var handles = flatten(slice.call(arguments));
+    var handles = slice.call(arguments).flat(Infinity);
 
     for (var i = 0; i < handles.length; i++) {
       var handle = handles[i];

lib/utils.js

@@ -16,7 +16,6 @@ var Buffer = require('safe-buffer').Buffer
 var contentDisposition = require('content-disposition');
 var contentType = require('content-type');
 var deprecate = require('depd')('express');
-var flatten = require('array-flatten');
 var mime = require('send').mime;
 var etag = require('etag');
 var proxyaddr = require('proxy-addr');
@@ -59,17 +58,6 @@ exports.isAbsolute = function(path){
   if ('\\\\' === path.substring(0, 2)) return true; // Microsoft Azure absolute path
 };
 
-/**
- * Flatten the given `arr`.
- *
- * @param {Array} arr
- * @return {Array}
- * @api private
- */
-
-exports.flatten = deprecate.function(flatten,
-  'utils.flatten: use array-flatten npm module instead');
-
 /**
  * Normalize the given `type`, for example "html" becomes "text/html".
  *

package.json

@@ -29,7 +29,6 @@
   ],
   "dependencies": {
     "accepts": "~1.3.8",
-    "array-flatten": "1.1.1",
     "body-parser": "1.20.2",
     "content-disposition": "0.5.4",
     "content-type": "~1.0.4",

test/utils.js

@@ -86,18 +86,3 @@ describe('utils.isAbsolute()', function(){
     assert(!utils.isAbsolute('foo/bar'));
   })
 })
-
-describe('utils.flatten(arr)', function(){
-  it('should flatten an array', function(){
-    var arr = ['one', ['two', ['three', 'four'], 'five']];
-    var flat = utils.flatten(arr)
-
-    assert.strictEqual(flat.length, 5)
-    assert.strictEqual(flat[0], 'one')
-    assert.strictEqual(flat[1], 'two')
-    assert.strictEqual(flat[2], 'three')
-    assert.strictEqual(flat[3], 'four')
-    assert.strictEqual(flat[4], 'five')
-    assert.ok(flat.every(function (v) { return typeof v === 'string' }))
-  })
-})