Fix negation operator

Author: brianmhunt

CHANGELOG.md

@@ -3,6 +3,7 @@ For TODO between alpha and release, see https://github.com/knockout/tko/issues/1
 
 ##  🏹  Alpha-1  ( Work in progress on the `master` branch )
 
+* Fix negation operator (-) application - integers `-1` work, as well as variables `-x` and expressions `-(x + y)`
 * Use tko.binding.foreach for the `foreach` binding (based on brianmhunt/knockout-fast-foreach)
 * Add `each` as an alias of `foreach`
 

dist/ko.js

@@ -3162,7 +3162,7 @@ var operators$1 = {
   '%': function mod(a, b) { return a % b; },
   // sub/add
   '+': function add(a, b) { return a + b; },
-  '-': function sub(a, b) { return a - b; },
+  '-': function sub(a, b) { return (a || 0) - (b || 0); },
   // relational
   '<': function lt(a, b) { return a < b; },
   '<=': function le(a, b) { return a <= b; },
@@ -4074,7 +4074,7 @@ Parser.prototype.expression = function (filterable) {
       break;
     }
 
-    // infix operators
+    // infix or postfix operators
     op = this.operator(true);
 
     if (op === operators['?']) {

dist/tko.js

@@ -3162,7 +3162,7 @@ var operators$1 = {
   '%': function mod(a, b) { return a % b; },
   // sub/add
   '+': function add(a, b) { return a + b; },
-  '-': function sub(a, b) { return a - b; },
+  '-': function sub(a, b) { return (a || 0) - (b || 0); },
   // relational
   '<': function lt(a, b) { return a < b; },
   '<=': function le(a, b) { return a <= b; },
@@ -4074,7 +4074,7 @@ Parser.prototype.expression = function (filterable) {
       break;
     }
 
-    // infix operators
+    // infix or postfix operators
     op = this.operator(true);
 
     if (op === operators['?']) {