meteor/meteor · error · Error

You must provide a valid topic to create a subscription.

Error message

You must provide a valid topic to create a subscription.

What it means

amplify.subscribe() requires its first argument (the topic) to be a string. The signature is (topic, context, callback, priority) with flexible argument handling, but the topic gate is strict. A non-string topic throws before the subscription is registered. amplify is a deprecated vendored library.

Source

Thrown at packages/deprecated/amplify/amplify.js:45

		if ( !subscriptions[ topic ] ) {
			return true;
		}

		topicSubscriptions = subscriptions[ topic ].slice();
		for ( length = topicSubscriptions.length; i < length; i++ ) {
			subscription = topicSubscriptions[ i ];
			ret = subscription.callback.apply( subscription.context, args );
			if ( ret === false ) {
				break;
			}
		}
		return ret !== false;
	},

	subscribe: function( topic, context, callback, priority ) {
		if ( typeof topic !== "string" ) {
			throw new Error( "You must provide a valid topic to create a subscription." );
		}

		if ( arguments.length === 3 && typeof callback === "number" ) {
			priority = callback;
			callback = context;
			context = null;
		}
		if ( arguments.length === 2 ) {
			callback = context;
			context = null;
		}
		priority = priority || 10;

		var topicIndex = 0,
			topics = topic.split( /\s/ ),
			topicLength = topics.length,
			added;
		for ( ; topicIndex < topicLength; topicIndex++ ) {

View on GitHub (pinned to 5076d2f818)

Solutions

1. Validate/coerce the topic to a string before subscribing.
2. Consider replacing amplify subscriptions with Tracker/ReactiveVar or a modern event emitter.

Example fix

// before
amplify.subscribe(config.channel, ctx, handler); // config.channel undefined -> throws

// after
if (typeof config.channel === 'string') {
  amplify.subscribe(config.channel, ctx, handler);
}

function safeSubscribe(topic, context, callback, priority) {
  if (typeof topic !== 'string' || !topic) {
    throw new TypeError('amplify.subscribe requires a non-empty string topic');
  }
  return amplify.subscribe(topic, context, callback, priority);
}

function isTopic(v) { return typeof v === 'string' && v.length > 0; }

When it happens

Trigger: amplify.subscribe(null, cb); amplify.subscribe(someNumber, ctx, fn); a topic variable that failed to resolve to a string.

Common situations: Subscribing with a dynamic topic from config/user input that is not validated; refactor that introduced an undefined topic; legacy code still on amplify.

Related errors

• You must provide a valid topic to publish.
• You must provide a valid topic to remove a subscription.
• Invalid AppCache config option: ${option}
• Can't add an invalid model to a collection
• Backbone.history has already been started

AI-assisted analysis of meteor/meteor@5076d2f818 (2026-08-13). Data as JSON: /api/errors/c05fde0d292e0795. Report an issue: GitHub.