Как передать переменную средставми webpack в скрипт?

const Elixir = require('laravel-elixir');
const webpack = require('webpack');
require('laravel-elixir-webpack-official');
require('laravel-elixir-vue-2');

Elixir.webpack.config.plugins   =   [
    new webpack.DefinePlugin({
        'process.env': {
            'API_URL': JSON.stringify("http://domain.com/api_url")
        }
    })
];

Elixir(
    mix => {
        mix.webpack('./src/app.js', publicPath),
            mix.copy(nodeModulesPath+"/font-awesome/fonts/",publicPath+"/fonts/")
    }
);

mounted(){
        console.log(process.env.API_URL); // undefined
    }