In ES6, export let m = 1; and m =1 expoort m ; why the former is true, the latter is false? : ```
 export let m = 1; 
```

```
let m =1; 
expoort m; 

```
I know the export of ES6 Module need to be an interface. The former export an interface,and the latter export number 1.
I want to know why the former export an interface? I guess priority of operations, but I am not sure.
Thanks. 
