Pass variable to _document.js from server.js

[blackbing]

Can I pass some variable from create next? for example

const app = next({ dev: isDev, customProps: { GA_ID: 'UA_XXXXXX' });

then I can get this GA_ID variable in _document.js and render it.

I know universal-config provide another way to handle it, but it will be replaced in the build time. If I have several different environment. I have to build by different config. So I hope I can pass variable to render _document.js

related issue is #159 but as I mentioned above, universal-config will replace variable in the build time instead of run time. so I hope there is a better way to do that.

• I have searched the issues of this repository and believe that this is not a duplicate.

[blackbing]

@timneutkens thanks for your example. I understand you export env config to windows.__ENV__.
I use https://github.com/mozilla/node-convict to configure my env variable. Consider this example code.

var convict = require('convict');

// Define a schema
var config = convict({
  API_URL: {
    doc: "API_URL.",
    format: String,
    default: "127.0.0.1",
    env: "API_URL",
  },
});
// Load environment dependent configuration
var env = config.get('env');
config.loadFile('./config/' + env + '.json');

// Perform validation
config.validate({allowed: 'strict'});

It loads the file and do some validate. however it cannot be executed on client side. The env config should be decided on server side, and I can decided what I should export to client side. So I am curious about if I make this variable from create next.

const app = next({ dev: isDev, customProps: { GA_ID: 'UA_XXXXXX' });

Is it possible?

[timneutkens]

@blackbing _document.js is executed only on the server. Only the API_URL environment variable is exposed https://github.com/zeit/next.js/pull/3371/files#diff-bc9a93f185c52580e4adb7607bc35ddaR5. You can put the convict code in _document.js and it'll work just fine 👍

[misuzu]

@timneutkens
When running like this it does not work properly:

npm run build
API_URL='https://example.com' npm run start

This is needed when building on CI server and running resulting build on many environments with different configuration.

[timneutkens]

Use this: https://github.com/zeit/next.js#exposing-configuration-to-the-server--client-side