SyntaxError: Cannot use import statement outside a module

问题

I've got an ApolloServer project that's giving me trouble, so I thought I might update it and ran into issues when using the latest Babel. My "index.js" is:

require('dotenv').config()
import {startServer} from './server'
startServer()

And when I run it I get the error "SyntaxError: Cannot use import statement outside a module". First I tried doing things to convince TPTB* that this was a module (with no success). So I changed the "import" to a "require" and this worked.

But now I have about two dozen "imports" in other files giving me the same error.

*I'm sure the root of my problem is that I'm not even sure what's complaining about the issue. I sort of assumed it was Babel 7 (since I'm coming from Babel 6 and I had to change the presets) but I'm not 100% sure.

Most of what I've found for solutions don't seem to apply to straight Node. Like this one here:

ES6 module Import giving "Uncaught SyntaxError: Unexpected identifier"

Says it was resolved by adding "type=module" but this would typically go in the HTML, of which I have none. I've also tried using my project's old presets:

"presets": ["es2015", "stage-2"],
"plugins": []

But that gets me another error: "Error: Plugin/Preset files are not allowed to export objects, only functions."

UPDATE: Here are the dependencies I started with:

"dependencies": {
"@babel/polyfill": "^7.6.0",
"apollo-link-error": "^1.1.12",
"apollo-link-http": "^1.5.16",
"apollo-server": "^2.9.6",
"babel-preset-es2015": "^6.24.1",

回答1:

2020 Update (Node 13.2.0+)

Verify that you have the latest version of Node installed. The --experimental-modules flag is no longer necessary. Simply do one of the following:

Add "type": "module" to the nearest parent package.json. With this, all .js and .mjs files are interpreted as ES modules. You can interpret individual files as CommonJS by using the .cjs extension.

Explicitly name files with the .mjs extension. All other files, such as .js will be interpreted as CommonJS, which is the default if type is not defined in package.json.

回答2:

According to the official doc (https://nodejs.org/api/esm.html#esm_code_import_code_statements):

import statements are permitted only in ES modules. For similar functionality in CommonJS, see import().

To make Node treat your file as a ES module you need to (https://nodejs.org/api/esm.html#esm_enabling):

add "type": "module" to package.json
add "--experimental-modules" flag to the node call

回答3:

I had the same issue and the following has fixed it (using node 12.13.1):

Change .js files extension to .mjs
Add --experimental-modules flag upon running your app.
Optional: add "type": "module" in your package.json

more info: https://nodejs.org/api/esm.html

回答4:

I ran into the same issue and it's even worse: I needed both "import" and "require"

1) Some newer ES6 modules works only with import.
2) Some CommonJS works with require.

Here is what worked for me:
1) Turn your js file into .mjs as suggested in other answers
2) "require" is not defined with ES6 module, so you can define it this way:

import { createRequire } from 'module'
 const require = createRequire(import.meta.url);

now 'require' can be used in the usual way.

3) Use import for ES6 modules and require for commonJS.

Some useful links: node.js's own documentation. difference between import and require. Microsoft has some nice documentation about import

Hope this helps

David

回答5:

I had the same problem when I started to used babel... But later, I had a solution... I haven't had the problem anymore so far... Currently, Node v12.14.1, "@babel/node": "^7.8.4", I use babel-node and nodemon to execute (node is fine as well..)
package.json: "start": "nodemon --exec babel-node server.js "debug": "babel-node debug server.js" !!note: server.js is my entry file, you can use yours.
launch.json When you debug, you also need to config your launch.json file "runtimeExecutable": "${workspaceRoot}/node_modules/.bin/babel-node" !!note: plus runtimeExecutable into the configuration.
Of course, with babel-node, you also normally need and edit another file, such as babel.config.js/.babelrc file

回答6:

My solution was to include babel-node path while running nodemon as follows:

nodemon node_modules/.bin/babel-node index.js

you can add in your package.json script as :

debug: nodemon node_modules/.bin/babel-node index.js

NOTE: My entry file is index.js replace it with your entry file (many have app.js/server.js).

回答7:

I had this problem in a fledgling Express API project.

The offending server code in src/server/server.js:

import express from 'express';
import {initialDonationItems, initialExpenditureItems} from "./DemoData";

const server = express();

server.get('/api/expenditures', (req, res) => {
  res.type('json');
  res.send(initialExpenditureItems);
});

server.get('/api/donations', (req, res) => {
  res.type('json');
  res.send(initialDonationItems);
});

server.listen(4242, () => console.log('Server is running...'));

Here were my dependencies:

{
  "name": "contributor-api",
  "version": "0.0.1",
  "description": "A Node backend to provide storage services",
  "scripts": {
    "dev-server": "nodemon --exec babel-node src/server/server.js --ignore dist/",
    "test": "jest tests"
  },
  "license": "ISC",
  "dependencies": {
    "@babel/core": "^7.9.6",
    "@babel/node": "^7.8.7",
    "babel-loader": "^8.1.0",
    "express": "^4.17.1",
    "mysql2": "^2.1.0",
    "sequelize": "^5.21.7",
    "sequelize-cli": "^5.5.1"
  },
  "devDependencies": {
    "jest": "^25.5.4",
    "nodemon": "^2.0.3"
  }
}

And here was the runner that threw the error:

nodemon --exec babel-node src/server/server.js --ignore dist

This was frustrating, as I had a similar Express project that worked fine.

The solution was firstly to add this dependency:

npm install @babel/preset-env

And then to wire it in using a babel.config.js in the project root:

module.exports = {
  presets: ['@babel/preset-env'],
};

I don't fully grok why this works, but I copied it from an authoritative source, so I am happy to stick with it.

来源：https://stackoverflow.com/questions/58384179/syntaxerror-cannot-use-import-statement-outside-a-module

标签

javascript

node.js

babeljs

apollo-server