meteor/v3-docs/v3-migration-docs/api/environment-variables.md

Environment Variables

Meteor provides the Meteor.EnvironmentVariable class, which helps maintain context across different boundaries.

With Meteor 3.0, we added support for asynchronous flows and improved how context is managed. As a result, some packages began losing context data, as described in this issue.

If your app or package uses EnvironmentVariable, make sure to use EnvironmentVariable.withValue at the top level to correctly preserve and propagate the context.

For instance, when updating publish behavior and introducing a new EnvironmentVariable context, you need to adjust your code as follows:

const _publishConnectionId = new Meteor.EnvironmentVariable<
  string | undefined
  >();

// Before
function patchPublish(publish: typeof Meteor.publish) {
  return function (this: typeof Meteor, name, func, ...args) {
    return publish.call(
      this,
      name,
      function (...args) {
        return _publishConnectionId.withValue(this?.connection?.id, () =>
          func.apply(this, args),
        );
      },
      ...args,
    );
  } as typeof Meteor.publish;
}

// After
function patchPublish(publish: typeof Meteor.publish) {
  return function (this: typeof Meteor, name, func, ...args) {
    return _publishConnectionId.withValue(this?.connection?.id, () => {
      return publish.call(
        this,
        name,
        function (...args) {
          return func.apply(this, args);
        },
        ...args,
      );
    });
  } as typeof Meteor.publish;
}

This example demonstrates the migration applied to the universe:i18n package.