问题
There is a specific thing i want to do from time to time, that i cannot figure out:
suppose module1.js exports 3 values:
//module1.js
export const a = 'a';
export const b = 'b';
export const c = 'c';
And then, in module2.js, I want to import two of these, into an object (as a kind of namespace thing):
//module2.js
import { a, c } as constants from './module1'; //<-WRONG!
So what I end up doing is something like this:
//module2.js
import { a, c } from './module1';
const constants = { a, c };
This works, but now a and c exist both in constants and also directly in the module scope.
Is there a way to avoid this?
回答1:
As per MDN documentation, you can either set an alias on entire module contents such as * as constants or a single content such as b as constants. But you can't set an alias on specific contents. So one of the solutions would be using *.
import * as constants from './module1';
Another possible solution would be passing { a, c } as default.
//module1.js
export const a = ...
export const b = ...
export const c = ...
export const d = ...
export default { a, b, c };
/module2.js
import contants from './someModule';
doStuff(constatns);
Lastly, If you don't want to pass these constants as default, you can create an object and pass that object.
//module1.js
export const a = ...
export const b = ...
export const c = ...
export const b = ...
export const myCustomConstants = { a, c };
//module2.js
import { myCustomConstants } from './someModule';
doStuff(myCustomConstants);
回答2:
Do you mean something like
import * as constants from './module1';
You could also remove some if you need to pass them down, something like lodash pick
const cleanConstants = _.pick(['a', 'c'], constants);
来源：https://stackoverflow.com/questions/48935969/es6-import-specific-values-with-namespace