Laravel Mix: Configure Babel for IE11 compatibility (transformations and polyfills)

Question

In a Laravel 6 application with Laravel-Mix 4, and using the Vue preset, I need to compile my JavaScript code to be compatible for IE11. This means adding any polyfills for missing functions, compiling out arrow functions, and so on. Out of the box, this is not done.

My test code in resources/js/app.js:

//require('./bootstrap');
let test = [1, 2, [3, 4]];
console.log(
    test.flat().map((x) => 2*x)
);

With default config, laravel mix does not appear to compile JavaScript code, but only do some formatting. Comments are preserved in the compiled output.

The result of npm run dev is:

       Asset      Size   Chunks             Chunk Names
/css/app.css   0 bytes  /js/app  [emitted]  /js/app
  /js/app.js  4.95 KiB  /js/app  [emitted]  /js/app

How do I get Laravel-Mix to use Babel to create IE11-compatible source code?

Answer 1

Enable Babel compilation with Laravel Mix, and use polyfills for internet explorer

Step 1: Install Corejs to get polyfills

Following the Babeljs docs for babel-preset-env 2, we first need to install core-js (which contains the polyfills):

$ npm install core-js@3 --save

Step 2: Configure .babelrc

create a .babelrc file in the project root:

{
    "presets": [
        [
            "@babel/preset-env",
            {
                "useBuiltIns": "usage",
                "corejs": {
                    "version": 3,
                    "proposals": false
                },
                "targets": {
                    "ie": "11"
                }
            }
        ]
    ]
}

Now run npm run dev and you will find polyfills inserted, arrow functions compiled out etc. - your code may just run on IE11!

Laravel-Mix, Babel, IE: Some gotchas

node_modules are not processed through babel

With the default configuration, only source code in the project itself - not its dependencies - runs through the babel compilation step. This means that any let or similar in the dependencies will trip up legacy browsers 3.

using `mix.babel' risks compiling a file twice

The laravel mix docs suggest using the mix.babel function in the Vanilla JS section 1. What this appears to do:

• if no .babelrc is present, the specified file is run through babel.
• if a .babelrc is present, the normal mix compilation step already uses babel. Using mix.babel causes the compilation step to be run twice.

Interestingly, the twice-compiled code does not run on IE. One problem is that it will contain require() calls for polyfills that cannot be handled:

SCRIPT5009: 'require' is undefined