问题
I'm using webpack with vuejs. Webpack does its thing, but when I look at the outputted app.js file, it gives me this error.
'import' and 'export' may only appear at the top level
I'm assuming it's a problem with babel not converting the code? Because I'm getting this in the browser when viewing the application.
Unexpected token import
Here's my entry.js for my vuejs application:
/*jshint esversion: 6 */
import Vue from 'vue';
import App from './App.vue';
import VueRouter from 'vue-router';
Vue.use(VueRouter);
require('./css/style.scss');
// Export the vue router
export var router = new VueRouter({
hashbang: false,
root: '/'
// history: true
});
// Set up routing and match routes to components
router.map({
'/': {
component: require('./components/home/Home.vue')
}
});
// Redirect to the home route if any routes are unmatched
router.redirect({
'*': '/'
});
// Start the app on the #app div
router.start(App, '#app');
Here's my webpack.config.js:
var ExtractTextPlugin = require('extract-text-webpack-plugin');
var path = require('path');
module.exports = {
entry: './src/entry.js',
output: {
filename: './public/js/app.js'
},
devtool: 'source-map',
plugins: [
new ExtractTextPlugin('./public/css/style.css')
],
module: {
preLoaders: [{
test: /\.js$/,
exclude: /node_modules/,
loader: 'jshint-loader'
}],
loaders: [{
test: /\.scss$/,
loader: ExtractTextPlugin.extract(
'style',
'css!sass'
),
},
{
test: /\.vue$/,
loader: 'vue'
},
{
test: /\.js$/,
exclude: /node_modules/,
include: [
path.resolve(__dirname, "src/services"),
],
loader: 'babel-loader',
query: {
presets: ['es2015']
}
}]
}
};
Here's my packages.json file:
{
"name": "test-webpack",
"version": "1.0.0",
"description": "Myapp",
"main": "entry.js",
"scripts": {
"watch": "webpack-dev-server --host $IP --port $PORT --hot --inline --config webpack.config.js",
"dev": "webpack",
"build": ""
},
"author": "Dev",
"license": "ISC",
"devDependencies": {
"babel-core": "^6.9.1",
"babel-loader": "^6.2.4",
"babel-plugin-transform-class-properties": "^6.10.2",
"babel-plugin-transform-runtime": "^6.9.0",
"babel-preset-es2015": "^6.9.0",
"babel-runtime": "^6.9.2",
"css-loader": "^0.23.1",
"extract-text-webpack-plugin": "^1.0.1",
"jshint": "^2.9.2",
"jshint-loader": "^0.8.3",
"node-sass": "^3.8.0",
"path": "^0.12.7",
"sass-loader": "^3.2.0",
"style-loader": "^0.13.1",
"vue-hot-reload-api": "^1.3.2",
"vue-html-loader": "^1.2.2",
"vue-loader": "^8.5.2",
"vue-style-loader": "^1.0.0",
"webpack": "^1.13.1",
"webpack-dev-server": "^1.14.1"
},
"dependencies": {
"vue": "^1.0.25",
"vue-router": "^0.7.13"
}
}
回答1:
'import' and 'export' may only appear at the top level
This means that webpack is bundling the non-transpiled ES6 code, which is why these import/export statements are being found. babel-loader must therefore not be transpiling what you expect.
If you simply remove the include and exclude rules from its loader config, the default behavior of transpiling everything besides what's in node_modules will kick in. For some reason or another, the current rules are causing some/all files to be skipped.
module.exports = {
entry: './src/entry.js',
output: {
filename: './public/js/app.js'
},
devtool: 'source-map',
plugins: [
new ExtractTextPlugin('./public/css/style.css')
],
module: {
preLoaders: [{
test: /\.js$/,
exclude: /node_modules/,
loader: 'jshint-loader'
}],
loaders: [{
test: /\.scss$/,
loader: ExtractTextPlugin.extract(
'style',
'css!sass'
),
},
{
test: /\.vue$/,
loader: 'vue'
},
{
test: /\.js$/,
loader: 'babel-loader',
query: {
presets: ['es2015']
}
}]
}
};
回答2:
I got this error when I was missing a closing bracket.
Simplified recreation:
const foo = () => {
return (
'bar'
);
}; <== this bracket was missing
export default foo;
回答3:
Make sure you have a .babelrc file that declares what Babel is supposed to be transpiling. I spent like 30 minutes trying to figure this exact error. After I copied a bunch of files over to a new folder and found out I didn't copy the .babelrc file because it was hidden.
{
"presets": "es2015"
}
or something along those lines is what you are looking for inside your .babelrc file
回答4:
Using webpack 4.14.0 and babel-cli 6.26 I had to install this Babel plugin to fix the SyntaxError: 'import' and 'export' may only appear at the top level error: babel-plugin-syntax-dynamic-import
It was linked through from the Webpack Code Splitting Docs.
回答5:
Look out for a double opening bracket syntax error as well {{ which can cause this error message to appear
回答6:
I had the same issue using webpack4, i was missing the file .babelrc in the root folder:
{
"presets":["env", "react"],
"plugins": [
"syntax-dynamic-import"
]
}
From package.json :
"babel-core": "^6.26.3",
"babel-loader": "^7.1.5",
"babel-plugin-syntax-dynamic-import": "^6.18.0",
"babel-polyfill": "^6.26.0",
"babel-preset-env": "^1.7.0",
"babel-preset-react": "^6.24.1",
回答7:
I got this error after upgrading to webpack 4.29.x. It turned out that webpack 4.29.x triggered npm's peerDependency bug. And according to them, the bug is not going to get fixed soon. Here's the workaround from sokra
- add
"acorn": "^6.0.5"to your application package.json. - Switch to
yarn. It doesn't have this bug. npm update acorn --depth 20npm dedupe(works only in some cases)rm package-lock.jsonnpm i(works only in some cases)- update all other packages that depend on an older version for acorn (works only in some cases)
- lock webpack at
4.28.4in your package.json
Update
According to comment below, this bug doesn't exist anymore after 4.36.0
回答8:
My error is caused by a System.import('xxx.js') statment. After replacing it with import xxx from 'xxx.js', the error solved.
I think it is because require('xxx.scss') also caused a dynamic import.
For the case in the question description, in my opinion, dynamic imports is not necessary, so the problem should be solved by just replacing all requires with import ... from ....
For some case which dynamic imports are necessary, you may need @babel/plugin-syntax-dynamic-import as other answers in this question.
回答9:
I am using Webpack 2.2.0 to bundle my React JS modules.
Encountered a similar issue while importing modules in my main app.js file.
After 30 minutes of headbanging I updated the RegEx for testing the file types in my webpack.config.js.
Carefully notice the ? symbol in test RegEx query.
{
test: /\.js?$/,
exclude: /(node_modules)/,
loader: 'react-hot-loader'
}
It worked for me !!
回答10:
I do not know how to solve this problem differently, but this is solved simply. The loader babel should be placed at the beginning of the array and everything works.
回答11:
Vue supports async components:
Source : https://vueschool.io/articles/vuejs-tutorials/async-vuejs-components/
<script>
export default {
data: () => ({ show: false }),
components: {
Tooltip: () => import("./Tooltip")
}
};
</script>
Good Luck...
回答12:
Maybe you're missing some plugins, try:
npm i --save-dev babel-plugin-transform-vue-jsx
npm i --save-dev babel-plugin-transform-runtime
npm i --save-dev babel-plugin-syntax-dynamic-import
- If using "Webpack.config.js":
- If using ".babelrc", see answer in this link.
回答13:
This is not direct answer to the original question but I hope this suggestion helps someones with similar error:
When using a newer web-api with Webpack+Babel for transpiling and you get
Module parse failed: 'import' and 'export' may only appear at the top level
then you probably forgot to import a polyfill.
For example:
when using fetch() api and targeting for es2015, you should
- add
whatwg-fetchpolyfill to package.json - add
import {fetch} from 'whatwg-fetch'
回答14:
I got this error when I was missing a closing brace in a component method:
const Whoops = props => {
const wonk = () => {props.wonk(); // <- note missing } brace!
return (
<View onPress={wonk} />
)
}
来源：https://stackoverflow.com/questions/37902849/import-and-export-may-only-appear-at-the-top-level