Babel JS -- simply convert JavaScript STRING to es5 (USING nodejs)

Question

I've been googling a lot and found a lot of half-answers or answers that don't address my question, so:

I'm just trying to take an input string, that string being regular-source javascript code (NOT nodejs, JUST regular JavaScript) and convert that into another STRING (not a file) that contains browser-compatible JavaScript (es5 or whatever).

I'm NOT trying to run nodejs as es5, and I'm not trying to convert a single file, I want to take a string of newer JavaScript and get a string of older JavaScript.

Now, using the BabelJS docs, it says to do this:

babel.transform(code, options, function(err, result) {
  result; // => { code, map, ast }
});

After making a .babelrc file with this in it (and npm install @babel/preset-env --save-dev):

{
  "presets": ["@babel/preset-env"]
}

But on the docs it doesn't say what "options" should be just to get it working.

A bunch of other posts on here said to include npm install babel-preset-es2015 and

module: {
    loaders: [
      {
        test: /\.js$/,
        loader: 'babel-loader?presets[]=es2015'
      }
    ]
  }

But I think that's for an older version which doesn't work anymore

and this famous answer gives this as a solution:

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" } }],
    ]
}

But that's just making a new javascript FILE I just simply want to make a string from another string.

I think I need to use Babel 7 as that's the newest version, but I keep getting various console errors..

Can someone just provide a simple step-by-step process for getting babel (preferably 7) to convert a string of newer JavaScript to a string of older?

Answer 1

I'm not certain if this is what you've expected.

I have this simple project structure:

-- package.json
-- index.js
-- .babelrc

index.js

let babel = require('@babel/core')

// some es6 code
let code = `
    let a = () => { console.log('hello') }
`
babel.transform(
    code,
    {
        babelrc: true,
        filename: '.babelrc'
    },
    function(err, result) {
        console.log(result.code)
    }
)

and this is the console output:

D:\Documents\code\test>node index.js
"use strict";

var a = function a() {
  console.log('hello');
};

D:\Documents\code\test>

and my .babelrc & package.json files in case you're interested.

{
    "presets": [
        "@babel/preset-env"
    ]
}

I just followed along the usage guide. In this case, polyfill and cli are not required.

{
  "name": "test",
  "version": "1.0.0",
  "dependencies": {
    "@babel/polyfill": "^7.2.5"
  },
  "devDependencies": {
    "@babel/cli": "^7.2.3",
    "@babel/core": "^7.3.4",
    "@babel/preset-env": "^7.3.4"
  }
}