beforeMigration option

[Ciberusps]

You can use beforeMigration callback for logging purposes, preparing migration data, etc.
beforeMigration callback will be called before the migration is executed.
It could be useful when u have multiple configs and you want to log the migration data for each config.

My example - I use multiple electron-store's and its usefull to log all migrations via electron-log in single file for debugging purposes, its easier to understand what can cause issue. Probably its can be usefull for others

import Conf from 'conf';

console.log = someLogger.log;

const mainConfig = new Conf({
	beforeMigration: (store, currentVersion, nextVersion) => {
		console.log(`[main-config] migrate from ${currentVersion} -> ${nextVersion}`);
	},
	migrations: {
		'0.4.0': store => {
		   // somethign that might broke config silently
        },
	}
});

const secondConfig = new Conf({
	beforeMigration: (store, currentVersion, nextVersion) => {
		console.log(`[second-config] migrate from ${currentVersion} -> ${nextVersion}`);
	},
	migrations: {
		'1.0.1': store => {
          // somethign that might broke config silently
        },
	}
});

[sindresorhus]

I would prefer if it were like this.

Suggested change

	beforeMigration: (store, currentVersion, nextVersion) => {
	beforeMigration: (store, context) => {

That way we could easily add more metadata properties in the future.

[sindresorhus]

Should the properties maybe be named fromVersion and toVersion? currentVersion makes it sound like it's the current version of the package, not the current version in the migration process.

[sindresorhus]

We could maybe also add the package version and all the migration versions. In case the user wants to know where in the migration process they are.

[Ciberusps]

We could maybe also add the package version and all the migration versions. In case the user wants to know where in the migration process they are.

Added context.migrationProcess with finalVersion and migrations not sure how to name them properly probably they can be flattened and lay in context but proper naming required

[sindresorhus]

I would prefer to keep them top-level in context (no nesting).

[sindresorhus]

This is ambiguous. Before the whole process or before each step.

[sindresorhus]

Suggested change

	store.set(`beforeMigration ${currentVersion} -> ${nextVersion}`, true);
	store.set(`beforeMigration ${currentVersion} → ${nextVersion}`, true);

[sindresorhus]

I think it should be called beforeEachMigration to make it clear it's called for each step and that would also allow adding a beforeMigration hook in the future which would be called only once before all migrations are done.

[sindresorhus]

Suggested change

	*/
	*/

[sindresorhus]

Suggested change

	console.log(`[main-config] final migration verison ${context.migrationProcess.finalVersion}, all migrations that were run or will be runned: ${context.migrationProcess.versions.toString()}`);
	console.log(`[main-config] final migration version ${context.migrationProcess.finalVersion}, all migrations that were run or will be ran: ${context.migrationProcess.versions.toString()}`);

[sindresorhus]

Use t.true