ES6 variable import name in node.js?

Solution 1:

Not with the import statement. import and export are defined in such a way that they are statically analyzable, so they cannot depend on runtime information.

You are looking for the loader API (polyfill), but I'm a bit unclear about the status of the specification:

System.import('./utils/' + variableName).then(function(m) {
  console.log(m);
});

Solution 2:

Whilst this is not actually a dynamic import (eg in my circumstance, all the files I'm importing below will be imported and bundled by webpack, not selected at runtime), a pattern I've been using which may assist in some circumstances is:

import Template1 from './Template1.js';
import Template2 from './Template2.js';

const templates = {
  Template1,
  Template2
};

export function getTemplate (name) {
  return templates[name];
}

or alternatively:

// index.js
export { default as Template1 } from './Template1';
export { default as Template2 } from './Template2';


// OtherComponent.js
import * as templates from './index.js'
...
// handy to be able to fall back to a default!
return templates[name] || templates.Template1;

I don't think I can fall back to a default as easily with require(), which throws an error if I try to import a constructed template path that doesn't exist.

Good examples and comparisons between require and import can be found here: http://www.2ality.com/2014/09/es6-modules-final.html

Excellent documentation on re-exporting from @iainastacio: http://exploringjs.com/es6/ch_modules.html#sec_all-exporting-styles

I'm interested to hear feedback on this approach :)

Solution 3:

In addition to Felix's answer, I'll note explicitly that this is not currently allowed by the ECMAScript 6 grammar:

ImportDeclaration :

import ImportClause FromClause ;

import ModuleSpecifier ;

FromClause :

from ModuleSpecifier

ModuleSpecifier :

StringLiteral

A ModuleSpecifier can only be a StringLiteral, not any other kind of expression like an AdditiveExpression.

Solution 4:

There is a new specification which is called a dynamic import for ES modules. Basically, you just call import('./path/file.js') and you're good to go. The function returns a promise, which resolves with the module if the import was successful.

async function importModule() {
   try {
      const module = await import('./path/module.js');
   } catch (error) {
      console.error('import failed');
   }
}

Use cases

Use-cases include route based component importing for React, Vue etc and the ability to lazy load modules, once they are required during runtime.

Further Information

Here's is an explanation on Google Developers.

Browser compatibility (April 2020)

According to MDN it is supported by every current major browser (except IE) and caniuse.com shows 87% support across the global market share. Again no support in IE or non-chromium Edge.