`export default` problems

[kimjoar]

I've found some potential bugs that works with Babel 5, but correctly breaks with Babel 6.

module.exports and exports default are different in some important ways, e.g. that this isn't allowed:

// foo.js
export default { baz: 42, bar: false }

// bar.js
import { baz } from './foo'

Instead it should be:

export const baz = 42;
export const bar = false;

I see we export an object several places:

$ find ./src -name "*.js" | xargs grep -l "export default {"
./src/cli/plugin/plugin_installer.js
./src/fixtures/field_mapping.js
./src/fixtures/filter_skeleton.js
./src/fixtures/mapping_with_dupes.js
./src/fixtures/mock_ui_state.js
./src/fixtures/search_response.js
./src/plugins/kibana/public/discover/components/field_chooser/lib/field_calculator.js
./src/plugins/kibana/public/settings/saved_object_registry.js
./src/ui/public/modules.js
./src/ui/public/utils/date_range.js
./src/ui/public/utils/dateMath.js
./src/ui/public/utils/key_map.js
./src/ui/public/utils/sequencer.js
./src/ui/public/utils/supports.js

We should probably go through these exports and fix them. We might need smarter search too, in order to catch things like:

// foo.js
const obj = { baz: 42, bar: false };
export default obj;

// bar.js
import { baz } from './foo'

Might be possible to use jscodeshift, jsfmt or something else to search for it (or just upgrade and see where it breaks 🙈)

[epixa]

Can you export an object as default so long as you import the whole object?

[spalger]

@epixa yes

[epixa]

In that case, we may not want to outright change all default object exports and instead just fix the instances there we import only a portion of the object. For things like configuration blocks, it's entirely reasonable to use export default.

[spalger]

or we could move to named exports everywhere and use import * as name from 'module'; where we want the whole object.

[spalger]

Or, if you really need to export a dynamic object:

export const config = {
  // my config
};

and

import { config: { name } } from './config';

[kimjoar]

@spalger Sure about this one?

import { config: { name } } from './config';

From https://tc39.github.io/ecma262/#sec-imports I can't get that one to go up (ImportsList doesn't contain NamedImports). And Babel gives me the error message

SyntaxError: index.js: Unexpected token (1:15)

[kimjoar]

Btw, several of the fixtures files could potentially be .json files instead, and have no export default.

[kimjoar]

Closing as we're now on 6