How to import everything exported from a file with ES2015 syntax? Is there a wildcard?

问题

With ES2015 syntax, we have the new import syntax, and I've been trying to figure out how to import everything exported from one file into another, without having it wrapped in an object, ie. available as if they were defined in the same file.

So, essentially, this:

// constants.js

const MYAPP_BAR = 'bar'
const MYAPP_FOO = 'foo'

// reducers.js

import * from './constants'

console.log(MYAPP_FOO)

This does not work, at least according to my Babel/Webpack setup, this syntax is not valid.

Alternatives

This works (but is long and annoying if you need more than a couple of things imported):

// reducers.js

import { MYAPP_BAR, MYAPP_FOO } from './constants'

console.log(MYAPP_FOO)

As does this (but it wraps the consts in an object):

// reducers.js

import * as consts from './constants'

console.log(consts.MYAPP_FOO)

Is there a syntax for the first variant, or do you have to either import each thing by name, or use the wrapper object?

回答1:

Is there a syntax for the first variant,

No.

or do you have to either import each thing by name, or use the wrapper object?

Yes.

回答2:

You cannot import all variables by wildcard for the first variant because it causes clashing variables if you have it with the same name in different files.

//a.js
export const MY_VAR = 1;

//b.js
export const MY_VAR = 2;


//index.js
import * from './a.js';
import * from './b.js';

console.log(MY_VAR); // which value should be there?

Because here we can't resolve the actual value of MY_VAR, this kind of import is not possible.

For your case, if you have a lot of values to import, will be better to export them all as object:

// reducers.js

import * as constants from './constants'

console.log(constants.MYAPP_FOO)

回答3:

well you could import the object, iterate over its properties and then manually generate the constants with eval like this

import constants from './constants.js'

for (const c in constants) {
  eval(`const ${c} = ${constants[c]}`)
}

unfortunately this solution doesn't work with intellisense in my IDE since the constants are generated dynamically during execution. But it should work in general.

回答4:

Sure there are.

Just use codegen.macro

codegen
      'const { ' + Object.keys(require('./path/to/file')).join(',') + '} = require("./path/to/file");

But it seems that you can't import variable generated by codegen. https://github.com/kentcdodds/babel-plugin-codegen/issues/10

来源：https://stackoverflow.com/questions/35554526/how-to-import-everything-exported-from-a-file-with-es2015-syntax-is-there-a-wil

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javascript

ecmascript-6

es6-module-loader