using `config. ... ` to initialize a module config variable value in `config.js` fails

[sdetweil]

module config

		module: 'MMM-PrayerTime',
		position: 'top_left',
		config: {
			apiVersion: '1.0', // please, leave unchanged. reserved for future use.
			lat: '29.955271', // latitude of your position (city)
			lon: '31.215639', // longitude of your position (city)
			timezone: "Africa/Cairo", // please refer to http://php.net/manual/en/timezones.php
			timeFormat: 12,
			method: 5,
			playAdzan: ['fajr', 'dhuhr', 'asr', 'maghrib', 'isha'],
			notDisplayed: ['midnight', 'sunset'],
			useUpdateInterval: true,
			updateInterval: 86400 * 1000, // How often do you want to fetch new praying time? (milliseconds)
			animationSpeed: 2.5 * 1000, // Speed of the update animation. (milliseconds)
			language: config.language,  //  ------ this line causes failure 
			showAdzanAlert: true,
			showTomorrow: true,
			vertical: true, // set false for horizontal view
			alertTimer: 15000
			}
		},

used to work, fails with this error now

[05.06.2022 20:58.45.082] [LOG]   Loading config ...
[05.06.2022 20:58.45.088] [ERROR] [31mWARNING! Could not validate config file. Starting with default configuration. Please correct syntax errors at or above this line: ReferenceError: Cannot access 'config' before initialization[39m  <<<<<<<<<< points to language line
[31m    at Object.<anonymous> (/home/sam/MagicMirror.2.17.1/config/config.js:71:14)[39m
[31m    at Module._compile (node:internal/modules/cjs/loader:1116:14)[39m
[31m    at Object.Module._extensions..js (node:internal/modules/cjs/loader:1169:10)[39m
[31m    at Module.load (node:internal/modules/cjs/loader:988:32)[39m
[31m    at Module._load (node:internal/modules/cjs/loader:829:12)[39m
[31m    at Function.c._load (node:electron/js2c/asar_bundle:5:13331)[39m
[31m    at Module.require (node:internal/modules/cjs/loader:1012:19)[39m
[31m    at require (node:internal/modules/cjs/helpers:94:18)[39m
[31m    at loadConfig (/home/sam/MagicMirror.2.17.1/js/app.js:69:14)[39m
[31m    at App.start (/home/sam/MagicMirror.2.17.1/js/app.js:212:3)[39m

recreate add this module def into config.js start MM with npm start

were we depending on some lazy evaluation which doesn't exist anymore?

[sdetweil]

this fails on 2.18 and 2.19 (the folder is 2.17.1 but upgraded to 2.18)

[rejas]

what part of that config is the culprit? what does the config check script say?

[sdetweil]

I don't understand 1st part, I marked the line

    in the module config
         language:  config.language,

config:check finds no issue

[rejas]

sorry, didnt see that, my bad. do you know when it was the last time this worked?

config:check of course finds no issue since this is valid js, it cant do runtime checking of this (which might be a nice feature if it was possible. is it I ask myself?)

[sdetweil]

no idea. I need to look at age of module readme

why doesn't check use require()?

[sdetweil]

readme was last updated 2 years ago. so 2.19-8

2.10-2.11 for sure. but this is the first I've seen of this error. I know the module has been used since then, and there are others.

[rejas]

why doesn't check use require()?

do you mean for reading the config js file?

[sdetweil]

what is different about config:check usage of config.js vs runtime usage?

one works, the other doesn't

[khassel]

were we depending on some lazy evaluation which doesn't exist anymore?

I digged a bit into this and found that it has something to do with the changes from var to let.

If I change the content of config.js back to var config = { (from let config = {) the error is gone. It is still not usable because the config.language reference in the module is undefined which is may caused by other var/let changes in the source code.