Negative-integer keys on lists must be treated as object keys

lib/getObjectKeys.js

@@ -14,7 +14,7 @@ function getObjectKeys (obj, excludeListItemAccessorsBelowLength) {
     let accept = true
     if (excludeListItemAccessorsBelowLength > 0) {
       const index = Number(name)
-      accept = (index % 1 !== 0) || index >= excludeListItemAccessorsBelowLength
+      accept = !Number.isInteger(index) || index < 0 || index >= excludeListItemAccessorsBelowLength
     }
 
     if (accept && Object.getOwnPropertyDescriptor(obj, name).enumerable) {

test/compare.js

@@ -53,3 +53,16 @@ test('survives odd circular references', t => {
   foo2.foo = foo
   t.false(compare(foo, foo2).pass)
 })
+
+test('arrays are also compared by property', t => {
+  const a1 = [1, 2, 3]
+  a1.p = 'a1'
+  const a2 = [1, 2, 3]
+  a2.p = 'a2'
+  t.false(compare(a1, a2).pass)
+
+  const a3 = [1, 2, 3]
+  const a4 = [1, 2, 3]
+  a4[-1] = -1
+  t.false(compare(a3, a4).pass)
+})

test/format.js

@@ -160,10 +160,13 @@ test('formats a simple, nested array', t => {
 })
 
 test('formats an array with additional properties', t => {
-  const arr = ['foo', 'bar']
-  arr.baz = 'qux'
-  const actual = format(arr)
-  t.snapshot(actual)
+  const arr1 = ['foo', 'bar']
+  arr1.baz = 'qux'
+  t.snapshot(format(arr1))
+
+  const arr2 = [1, 2, 3]
+  arr2[-1] = -1
+  t.snapshot(format(arr2))
 })
 
 test('formats a multiline string inside an array', t => {

test/snapshots/format.js.md

@@ -359,6 +359,16 @@ Generated by [AVA](https://avajs.dev).
       baz%property.separator#: %%string.line.open#'%%string.open%qux%string.close%%string.line.close#'%%property.after#,%␊
     %list.closeBracket#]%`
 
+> Snapshot 2
+
+    `%list.openBracket#[%␊
+      %number.open%1%number.close%%item.after#,%␊
+      %number.open%2%number.close%%item.after#,%␊
+      %number.open%3%number.close%%item.after#,%␊
+      %stats.separator#---%␊
+      -1%property.separator#: %%number.open%-1%number.close%%property.after#,%␊
+    %list.closeBracket#]%`
+
 ## formats anonymous functions
 
 > Snapshot 1