> There was a SpiderMonkey bug1, and even a patch, for this for quite a while. The patch now landed and will be in Firefox 29.
 
>V8 got fixed last week too
>code.google.com/p/v8/issues/detail?id=3069

but according to spec, "forEach" should call callback with "-0":

var map = new Map();
map.set(-0, 'x');
map.forEach(function (value, key) {
  alert(1 / key);  
});
alert(map.get(0));

but according to spec, "forEach" should call callback with "-0":

```js
var map = new Map();
map.set(-0, 'x');
map.forEach(function (value, key) {
  alert(1 / key);  
});
alert(map.get(0));
```