[BUGFIX] Fix issue with with array constructor

- You can do new Array(4) to generate an array with 4 empty items
- Doing the same with list caused an error
- This broke lodash.deepclone
- This PR restores compatibility with the array constructor

Fixes #1798

lib/list.js

@@ -27,6 +27,11 @@ function List(items, itemType, parent) {
     }
   }
 
+  if (typeof items === 'number') {
+    // trying to initialise empty array with a length
+    items = [...new Array(items)];
+  }
+
   const arr = [];
   arr.__proto__ = List.prototype;
 

test/list.test.js

@@ -38,6 +38,16 @@ function PhoneCtor(label, num) {
   this.num = num;
 }
 
+describe('Does not break default Array functionality', function() {
+  it('allows creating an empty length with a specified length', function() {
+    const list = new List(4);
+    list.should.be.an.instanceOf(Array);
+    list.length.should.be.eql(4);
+    should.not.exist(list.itemType);
+    list.toJSON().should.eql([undefined, undefined, undefined, undefined]);
+  });
+});
+
 describe('list of items typed by a class', function() {
   it('allows itemType to be a class', function() {
     const phones = givenPhones();