Pierce01/MinecraftLauncher-core

const { Client, Authenticator } = require('minecraft-launcher-core');
const launcher = new Client();

let opts = {
    // For production launchers, I recommend not passing 
    // the getAuth function through the authorization field and instead
    // handling authentication outside before you initialize
    // MCLC so you can handle auth based errors and validation!
    authorization: Authenticator.getAuth("username", "password"),
    root: "./minecraft",
    version: {
        number: "1.14",
        type: "release"
    },
    memory: {
        max: "6G",
        min: "4G"
    }
}

launcher.launch(opts);

launcher.on('debug', (e) => console.log(e));
launcher.on('data', (e) => console.log(e));

let opts = {
   otherOps...,
   overrides: {
       gameDirectory: '', // where the game process generates folders like saves and resource packs.
       minecraftJar: '',
       versionJson: '',
       directory: '', // where the Minecraft jar and version json are located.
       natives: '', // native directory path.
       assetRoot: '',
       assetIndex: '',
       libraryRoot: '',
       cwd: '', // working directory of the java process.
       detached: true, // whether or not the client is detached from the parent / launcher.
       classes: [], // all class paths are required if you use this.
       minArgs: 11, // The amount of launch arguments specified in the version file before it adds the default again
       maxSockets: 2, // max sockets for downloadAsync.
       // The following is for launcher developers located in countries that have the Minecraft and Forge resource servers
       // blocked for what ever reason. They obviously need to mirror the formatting of the original JSONs / file structures.
       url: {
           meta: 'https://launchermeta.mojang.com', // List of versions.
           resource: 'https://resources.download.minecraft.net', // Minecraft resources.
           mavenForge: 'http://files.minecraftforge.net/maven/', // Forge resources.
           defaultRepoForge: 'https://libraries.minecraft.net/', // for Forge only, you need to redefine the library url
                                                                // in the version json.
           fallbackMaven: 'https://search.maven.org/remotecontent?filepath='
       },
       // The following is options for which version of ForgeWrapper MCLC uses. This allows us to launch modern Forge.
       fw: {
        baseUrl: 'https://github.com/ZekerZhayard/ForgeWrapper/releases/download/',
        version: '1.5.1',
        sh1: '90104e9aaa8fbedf6c3d1f6d0b90cabce080b5a9',
        size: 29892,
      },
      logj4ConfigurationFile: ''
   }
}

{
    access_token: '',
    client_token: '',
    uuid: '',
    name: '',
    user_properties: '{}',
    meta: {
        type: 'mojang' || 'msa',
        demo: true || false, // Demo can also be specified by adding 'is_demo_user' to the options.feature array 
        // properties only exists for specific Minecraft versions.
        xuid: '',
        clientId: ''
    }
}