On Thu, Jun 19, 2014 at 1:23 PM, Chris Toshok <[email protected]> wrote:
> On Thu, Jun 19, 2014 at 6:57 AM, Erik Arvidsson <[email protected]> > wrote: > >> >> On Thu, Jun 19, 2014 at 6:41 AM, Calvin Metcalf <[email protected] >> > wrote: >> >>> One other option could be for import name from 'path' to resolve to the >>> module body there is no default export, thanks to the static analysis >>> you'll always know when default is present. >>> >> That is a refactoring hazard. If the module changes to add/remove the >> default export the import will still succeed but the value is either a >> module instance object or anything: >> >> // a.js >> export default class C { ... } >> >> // importer.js >> import A from './a'; >> new A(); >> >> Now a.js changes. >> >> // a.js V2 >> export class C { ... } >> >> // importer.js >> import A from './a'; >> new A(); // TypeError: A is not a function >> >> With this idea you cannot look at the import statement to see if the >> imported binding is a module instance object or not. >> >> > I think you're example misses one point - The module author changed the > exported api, going from exporting a function named C to exporting an > object with a property named C. Problems caused by this refactoring would > exist regardless of Calvin's suggestion. > With the current spec this is a compile time error since a.js (V2) does not export default. > > Calvin's suggestion would allow the following refactoring to be done by > the module author without impacting his users, something not possible with > current ES6: > > ```js > // a.js V1 > export default { C: class C { ... } } > But this is the thing we are trying hard to have people never do. > > // a.js V2 > export class C { ... } > ``` > > The refactoring hazard is real, but exists iff the module consumer uses > implicit exports (i.e. an Object.prototype method with the above default > export). This is another reason why the named export form is better - > everything is explicit. IMO the only good reason to use default export is > to export a single function. > > -chris > > -- erik
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