feat: accept comparator function as deterministic option (#49)

Accept `Array#sort(comparator)` comparator method as deterministic option value to use that comparator for sorting object keys.

```js
import { configure } from 'safe-stable-stringify'

const object = {
  a: 1,
  b: 2,
  c: 3,
}

const stringify = configure({
  deterministic: (a, b) => b.localeCompare(a)
})

stringify(object)
// '{"c": 3,"b":2,"a":1}'

index.d.ts

@@ -7,7 +7,7 @@ export function stringify(value: unknown, replacer?: ((key: string, value: unkno
 export interface StringifyOptions {
   bigint?: boolean,
   circularValue?: string | null | TypeErrorConstructor | ErrorConstructor,
-  deterministic?: boolean,
+  deterministic?: boolean | ((a: string, b: string) => number),
   maximumBreadth?: number,
   maximumDepth?: number,
   strict?: boolean,

index.js

@@ -32,11 +32,11 @@ function strEscape (str) {
   return JSON.stringify(str)
 }
 
-function insertSort (array) {
-  // Insertion sort is very efficient for small input sizes but it has a bad
+function insertSort (array, comparator) {
+  // Insertion sort is very efficient for small input sizes, but it has a bad
   // worst case complexity. Thus, use native array sort for bigger values.
-  if (array.length > 2e2) {
-    return array.sort()
+  if (array.length > 2e2 || comparator) {
+    return array.sort(comparator)
   }
   for (let i = 1; i < array.length; i++) {
     const currentValue = array[i]
@@ -97,6 +97,23 @@ function getCircularValueOption (options) {
   return '"[Circular]"'
 }
 
+function getDeterministicOption (options, key) {
+  let value
+  if (hasOwnProperty.call(options, key)) {
+    value = options[key]
+    if (typeof value === 'boolean') {
+      return value
+    }
+    if (typeof value === 'function') {
+      return value
+    }
+  }
+  if (value === undefined) {
+    return true
+  }
+  throw new TypeError(`The "${key}" argument must be of type boolean or comparator function`)
+}
+
 function getBooleanOption (options, key) {
   let value
   if (hasOwnProperty.call(options, key)) {
@@ -171,7 +188,8 @@ function configure (options) {
   }
   const circularValue = getCircularValueOption(options)
   const bigint = getBooleanOption(options, 'bigint')
-  const deterministic = getBooleanOption(options, 'deterministic')
+  const deterministic = getDeterministicOption(options, 'deterministic')
+  const comparator = typeof deterministic === 'function' ? deterministic : undefined
   const maximumDepth = getPositiveIntegerOption(options, 'maximumDepth')
   const maximumBreadth = getPositiveIntegerOption(options, 'maximumBreadth')
 
@@ -248,7 +266,7 @@ function configure (options) {
         }
         const maximumPropertiesToStringify = Math.min(keyLength, maximumBreadth)
         if (deterministic && !isTypedArrayWithEntries(value)) {
-          keys = insertSort(keys)
+          keys = insertSort(keys, comparator)
         }
         stack.push(value)
         for (let i = 0; i < maximumPropertiesToStringify; i++) {
@@ -447,7 +465,7 @@ function configure (options) {
           separator = join
         }
         if (deterministic) {
-          keys = insertSort(keys)
+          keys = insertSort(keys, comparator)
         }
         stack.push(value)
         for (let i = 0; i < maximumPropertiesToStringify; i++) {
@@ -551,7 +569,7 @@ function configure (options) {
           separator = ','
         }
         if (deterministic) {
-          keys = insertSort(keys)
+          keys = insertSort(keys, comparator)
         }
         stack.push(value)
         for (let i = 0; i < maximumPropertiesToStringify; i++) {

test.js

@@ -1303,3 +1303,44 @@ test('strict option replacer array', (assert) => {
 
   assert.end()
 })
+
+test('deterministic option possibilities', (assert) => {
+  assert.throws(() => {
+    // @ts-expect-error
+    stringify.configure({ deterministic: 1 })
+  }, {
+    message: 'The "deterministic" argument must be of type boolean or comparator function',
+    name: 'TypeError'
+  })
+
+  const serializer1 = stringify.configure({ deterministic: false })
+  serializer1(NaN)
+
+  const serializer2 = stringify.configure({ deterministic: (a, b) => a.localeCompare(b) })
+  serializer2(NaN)
+
+  assert.end()
+})
+
+test('deterministic default sorting', function (assert) {
+  const serializer = stringify.configure({ deterministic: true })
+
+  const obj = { b: 2, c: 3, a: 1 }
+  const expected = '{\n "a": 1,\n "b": 2,\n "c": 3\n}'
+  const actual = serializer(obj, null, 1)
+  assert.equal(actual, expected)
+
+  assert.end()
+})
+
+test('deterministic custom sorting', function (assert) {
+  // Descending
+  const serializer = stringify.configure({ deterministic: (a, b) => b.localeCompare(a) })
+
+  const obj = { b: 2, c: 3, a: 1 }
+  const expected = '{\n "c": 3,\n "b": 2,\n "a": 1\n}'
+  const actual = serializer(obj, null, 1)
+  assert.equal(actual, expected)
+
+  assert.end()
+})