Babel file is copied without being transformed

问题:

I have this code:

"use strict";

import browserSync from "browser-sync";
import httpProxy from "http-proxy";

let proxy = httpProxy.createProxyServer({});

and I have installed babel-core and babel-cli globally via npm. The point is when I try to compile with this on my terminal:

babel proxy.js --out-file proxified.js

The output file gets copied instead of compiled (I mean, it's the same as the source file).

What am I missing here?

回答1:

Babel is a transformation framework. Pre-6.x, it enabled certain transformations by default, but with the increased usage of Node versions which natively support many ES6 features, it has become much more important that things be configurable. By default, Babel 6.x does not perform any transformations. You need to tell it what transformations to run:

npm install babel-preset-env

and run

babel --presets env proxy.js --out-file proxified.js

or create a .babelrc file containing

{
    "presets": [
        "env"
    ]
}

and run it just like you were before.

env in this case is a preset which basically says to compile all standard ES* behavior to ES5. If you are using Node versions that support some ES6, you may want to consider doing

{
    "presets": [
        ["env", { "targets": { "node": "true" } }],
    ]
}

to tell the preset to only process things that are not supported by your Node version. You can also include browser versions in your targets if you need browser support.

回答2:

Most of these answers are obsolete. @babel/preset-env and "@babel/preset-react are what you need (as of July 2019).

回答3:

I had the same problem with a different cause:

The code I was trying to load was not under the package directory, and Babel does not default to transpiling outside the package directory.

I solved it by moving the imported code, but perhaps I could have also used some inclusion statement in the Babel configuration.

回答4:

First ensure you have the following node modules:

npm i -D webpack babel-core babel-preset-es2015 babel-preset-stage-2 babel-loader

Next, add this to your Webpack config file (webpack.config.js) :

// webpack.config.js
...
module  :  {
  loaders  :  [
    {
      test    :  /\.js$/,
      loader  :  'babel',
      exclude :  /node_modules/,
      options :  {
        presets  :  [ 'es2015', 'stage-2' ] // stage-2 if required
      } 
    } 
  ]
}
...

References:

• https://gist.github.com/Couto/6c6164c24ae031bff935
• https://github.com/babel/babel-loader/issues/214

Good Luck!

回答5:

As of 2020, Jan:

STEP 1: Install the Babel presets:

yarn add -D @babel/preset-env @babel/preset-react

STEP 2: Create a file: babelrc.js and add the presets:

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

STEP 3:- Install the babel-loader:

yarn add -D babel-loader

STEP 4:- Add the loader config in your webpack.config.js:

{
//...
  module: [
    rules: [
      test: /\.(js|mjs|jsx|ts|tsx)$/,
      loader: require.resolve('babel-loader')
    ]
  ]
//...
}

Good Luck...

回答6:

npm install --save-dev babel-preset-node5

npm install --save-dev babel-preset-react

...and then creating a .babelrc with the presets:

{
  "presets": [
    "node5",
    "react"
  ]
}

...resolved a very similar issue for me, with babel 3.8.6, and node v5.10.1

https://www.npmjs.com/package/babel-preset-node5
https://www.npmjs.com/package/babel-preset-react

回答7:

Same error, different cause:

Transpiling had worked before and then suddenly stopped working, with files simply being copied as is.

Turns out I opened the .babelrc at some point and Windows decided to append .txt to the filename. Now that .babelrc.txt wasn't recognized by babel. Removing the .txt suffix fixed that.

回答8:

fix your .babelrc

{
  "presets": [
    "react",
    "ES2015"
  ]
}

回答9:

In year 2018:

Install following packages if you haven't yet:

npm install babel-loader babel-preset-react

webpack.config.js

{
    test: /\.jsx?$/,
    exclude: /node_modules/,
    use: [
      {
        loader: 'babel-loader',
        options: {
          presets: ['es2015','react']  // <--- !`react` must be part of presets!
        }
      }
    ],
  }

回答10:

Ultimate solution

I wasted 3 days on this

import react from 'react' unexpected identifier

I tried modifying webpack.config.js and package.json files, and adding .babelrc, installing & updating packages via npm, I've visited many, many pages but nothing has worked.

---

What worked? Two words: npm start. That's right.

run the

npm start 

command in the terminal to launch a local server

...

(mind that it might not work straight away but perhaps only after you do some work on npm because before trying this out I had deleted all the changes in those files and it worked, so after you're really done, treat it as your last resort)

---

I found that info on this neat page. It's in Polish but feel free to use Google translate on it.