Importing node modules from root directory using e

问题:

I'm writing a node app with es6 using babel transpiler.

I have 2 files index.js & my-module.js on my root directory

- index.js
- my-module.js

my-module.js

export let myFunc = () => {
  console.log('myFunc was called!!!');
}

index.js

import {myFunc} from './my-module';
myFunc();

if I run the following line from the command line everything works as expected.

$ babel-node index.js >> myFunc was called!!!

but if I remove the dot when importing my-module:

import {myFunc} from '/my-module';
myFunc();

I'm getting an error:

Error: Cannot find module '/my-module'

Any reason why I can't import modules using an absolute path? anyway to change .babelrc config to support it?

Thanks

回答1:

Like (almost) any tool '/x' means 'x' in the root of your filesystem. Babel doesn't actually look at the paths, it just compiles

import {myFunc} from '/my-module';

into

var _myModule = require('/my-module');

And node actually looks up the module.

---

If you really want to import relative to the root of the project, you could use a plugin. I recommend using something that isn't very ambiguous, and make sure you document this for the next person reading your code!

Here's an example where we use a leading ~ to mean project relative. You could use anything you like e.g. ^ would also be good.

Example Input:

import {a} from '~my-module';
import {b} from '/my-module';
import {c} from './my-module';

scripts/babel-plugin-project-relative-require.js

module.exports = function (babel) {
  // get the working directory
  var cwd = process.cwd();

  return new babel.Transformer("babel-plugin-project-relative-require", {
    ImportDeclaration: function(node, parent) {
      // probably always true, but let's be safe
      if (!babel.types.isLiteral(node.source)) {
        return node;
      }

      var ref = node.source.value;

      // ensure a value, make sure it's not home relative e.g. ~/foo
      if (!ref || ref[0] !== '~' || ref[1] === '/') {
        return node;
      }

      node.source.value = cwd + '/' + node.source.value.slice(1);

      return node;
    }
  });
};

.babelrc

{
    "plugins": [
        "./scripts/babel-plugin-project-relative-require.js"
    ]
}

Output (if run in /tmp):

'use strict';

var _tmpMyModule = require('/tmp/my-module');

var _myModule = require('/my-module');

var _myModule2 = require('./my-module');

回答2:

The solution from FakeRainBrigand/Gavriguy is good and works well. So i decided to develop a plugin which you can easily install with npm in and use a simple Babel-Plugin.

https://github.com/michaelzoidl/babel-root-import

Hope this helps...

回答3:

First of all, Babel is just a transpiler from ES2015 to ES5 syntax. Its job is to transpile this:

import {myFunc} from '/my-module'

into this:

var _myModule = require('/my-module');

Actual module requiring performed by Node, and how Node does it you can read in details here: https://nodejs.org/api/modules.html#modules_file_modules

To summary, ./module means path to module relative to local directory, /module is an absolute path to module, module triggers Node to look for module in local node_modules directory and all ascending.