I'm trying to understand why this code snippet is not allowed: 

```
<tbody>{
for (var i=0; i < objects.length; i++) {
    <ObjectRow obj={objects[i]} key={i}>
} }

```

and why this one is allowed:

```
<tbody>
    {objects.map(function(object, i){
        return <ObjectRow obj={object} key={i} />;
    })}
</tbody

```

I'm not getting it...
Thanks for helping !