Given this:

```
let nums = [1,5,4]
let sorter = (a,b) => a.property > b.property ? 1 : -1;
let mapper = x => {return {property:x}}

```

This throws an error:

```
_.chain(nums).map(mapper).sortBy(sorter).value()
// Uncaught TypeError: Cannot read property 'property' of undefined

```

While this does not:

```
nums.map(mapper).sort(sorter)
// [{"property":1},{"property":4},{"property":5}]

```

What gives? Are we not guaranteed that `sortBy` will run after `map`? Or am I missing something truly obvious here?