fix: stable sort for undefined keys, fixes #191

src/builtin/filters/math.ts

@@ -1,4 +1,4 @@
-const toLowerCase = String.prototype.toLowerCase
+import { caseInsensitiveCompare } from '../../util/underscore'
 
 export default {
   'abs': (v: number) => Math.abs(v),
@@ -18,22 +18,12 @@ export default {
   'times': (v: number, arg: number) => v * arg
 }
 
-function caseInsensitiveCmp (a: any, b: any) {
-  if (!b) return -1
-  if (!a) return 1
-  a = toLowerCase.call(a)
-  b = toLowerCase.call(b)
-  if (a < b) return -1
-  if (a > b) return 1
-  return 0
-}
-
 function sortNatural (input: any[], property?: string) {
   if (!input || !input.sort) return []
   if (property !== undefined) {
     return [...input].sort(
-      (lhs, rhs) => caseInsensitiveCmp(lhs[property], rhs[property])
+      (lhs, rhs) => caseInsensitiveCompare(lhs[property], rhs[property])
     )
   }
-  return [...input].sort(caseInsensitiveCmp)
+  return [...input].sort(caseInsensitiveCompare)
 }

src/util/underscore.ts

@@ -1,6 +1,7 @@
 import { Drop } from '../drop/drop'
 
 const toStr = Object.prototype.toString
+const toLowerCase = String.prototype.toLowerCase
 
 /*
  * Checks if value is classified as a String primitive or object.
@@ -127,3 +128,15 @@ export function changeCase (str: string): string {
 export function ellipsis (str: string, N: number): string {
   return str.length > N ? str.substr(0, N - 3) + '...' : str
 }
+
+// compare string in case-insensitive way, undefined values to the tail
+export function caseInsensitiveCompare (a: any, b: any) {
+  if (a == null && b == null) return 0
+  if (a == null) return 1
+  if (b == null) return -1
+  a = toLowerCase.call(a)
+  b = toLowerCase.call(b)
+  if (a < b) return -1
+  if (a > b) return 1
+  return 0
+}