eth_getFilterChanges - Cronos RPC Method
Poll a filter for new results since the last poll on Cronos. Essential for event streaming, real-time monitoring, and efficient log indexing for DeFi protocols, NFT marketplaces, and Crypto.com ecosystem integrations.
Polls a filter on Cronos and returns an array of changes (logs, block hashes, or transaction hashes) that have occurred since the last poll. The return type depends on the filter that was created — log filters return log objects, block filters return block hashes, and pending transaction filters return transaction hashes.
Why Cronos? Build on the EVM-compatible Crypto.com blockchain with fast finality and deep Crypto.com ecosystem integration.
When to Use This Method
eth_getFilterChanges is essential for Cronos developers building DeFi and payment applications:
- Event Streaming — Incrementally consume new contract events without re-fetching the entire log history on Cronos
- Real-Time Monitoring — Track contract activity, token transfers, or governance votes for DeFi protocols, NFT marketplaces, and Crypto.com ecosystem integrations
- Efficient Log Indexing — Process only new events since your last poll, minimizing bandwidth and compute overhead
- Block & Transaction Tracking — When used with block or pending-transaction filters, detect new blocks or mempool activity in real time
Request Parameters
The filter ID returned by eth_newFilter, eth_newBlockFilter, or eth_newPendingTransactionFilter
Response Body
Address from which the log originated
Array of 0-4 indexed log arguments (32 bytes each)
Non-indexed log arguments (ABI-encoded)
Block number where the log was emitted
Hash of the transaction that generated the log
Index position of the transaction in the block
Hash of the block containing the log
Log index position in the block
true if the log was removed due to a chain reorganization
Array of 32-byte block hashes of new blocks
Array of 32-byte transaction hashes of pending transactions
Error Responses
Code Examples
curl -X POST https://api-cronos-mainnet-archive.n.dwellir.com/YOUR_API_KEY \
-H "Content-Type: application/json" \
-d '{
"jsonrpc": "2.0",
"method": "eth_getFilterChanges",
"params": ["0x1a"],
"id": 1
}'Common Use Cases
1. Real-Time Token Transfer Monitor
Stream ERC-20 transfer events on Cronos:
async function monitorTransfers(provider, tokenAddress) {
// Transfer event topic: keccak256('Transfer(address,address,uint256)')
const transferTopic = '0xddf252ad1be2c89b69c2b068fc378daa952ba7f163c4a11628f55a4df523b3ef';
const filterId = await provider.send('eth_newFilter', [{
fromBlock: 'latest',
address: tokenAddress,
topics: [transferTopic]
}]);
console.log(`Monitoring transfers on ${tokenAddress}...`);
setInterval(async () => {
try {
const logs = await provider.send('eth_getFilterChanges', [filterId]);
for (const log of logs) {
const from = '0x' + log.topics[1].slice(26);
const to = '0x' + log.topics[2].slice(26);
const value = BigInt(log.data);
console.log(`Transfer: ${from} -> ${to} (${value})`);
}
} catch (error) {
if (error.message.includes('filter not found')) {
console.log('Filter expired — recreating...');
// Filters expire after ~5 minutes of inactivity on most nodes
}
}
}, 3000);
}2. Multi-Contract Event Aggregator
Monitor events across multiple contracts simultaneously:
async function aggregateEvents(provider, contracts) {
const filterId = await provider.send('eth_newFilter', [{
fromBlock: 'latest',
address: contracts // Array of contract addresses
}]);
const eventBuffer = [];
let pollCount = 0;
const interval = setInterval(async () => {
const changes = await provider.send('eth_getFilterChanges', [filterId]);
pollCount++;
if (changes.length > 0) {
eventBuffer.push(...changes);
console.log(`Poll #${pollCount}: ${changes.length} new events (total: ${eventBuffer.length})`);
// Process in batches
if (eventBuffer.length >= 50) {
await processBatch(eventBuffer.splice(0, 50));
}
}
}, 2000);
return { filterId, stop: () => clearInterval(interval) };
}3. Block-Aware Event Processor with Reorg Handling
Detect chain reorganizations by checking the removed flag:
async function safeEventProcessor(provider, filterParams) {
const filterId = await provider.send('eth_newFilter', [filterParams]);
const processedEvents = new Map();
setInterval(async () => {
const changes = await provider.send('eth_getFilterChanges', [filterId]);
for (const log of changes) {
const eventKey = `${log.transactionHash}-${log.logIndex}`;
if (log.removed) {
// Chain reorganization — undo previously processed event
console.warn(`Reorg detected: removing event ${eventKey}`);
processedEvents.delete(eventKey);
await rollbackEvent(log);
} else {
processedEvents.set(eventKey, log);
await processEvent(log);
}
}
}, 2000);
}Error Handling
Common errors and solutions:
| Error Code | Description | Solution |
|---|---|---|
| -32000 | Filter not found | Filter expired or was uninstalled — recreate with eth_newFilter |
| -32600 | Invalid request | Verify the filter ID is correctly formatted as a hex string |
| -32603 | Internal error | Node may be overloaded — retry with exponential backoff |
| -32005 | Rate limit exceeded | Reduce polling frequency or implement client-side rate limiting |
async function resilientPoll(provider, filterId, createFilter, interval = 2000) {
let currentFilterId = filterId;
let retries = 0;
while (true) {
try {
const changes = await provider.send('eth_getFilterChanges', [currentFilterId]);
retries = 0;
if (changes.length > 0) {
return changes;
}
} catch (error) {
if (error.message.includes('filter not found')) {
console.log('Filter expired — recreating...');
currentFilterId = await createFilter();
} else if (error.code === -32005) {
const delay = Math.pow(2, retries) * 1000;
retries++;
await new Promise(r => setTimeout(r, delay));
} else {
throw error;
}
}
await new Promise(r => setTimeout(r, interval));
}
}Related Methods
eth_newFilter— Create a log/event filter to poll with this methodeth_newBlockFilter— Create a block filter for new block notificationseth_getFilterLogs— Get all logs matching a filter (full history, not incremental)eth_uninstallFilter— Remove a filter when no longer neededeth_getLogs— Query logs directly without creating a filter
eth_newFilter
Create an event log filter on Cronos. Essential for event monitoring, contract activity tracking, and DeFi event streaming for DeFi protocols, NFT marketplaces, and Crypto.com ecosystem integrations.
eth_getFilterLogs
Returns all logs matching a previously created filter on Cronos. Essential for initial log retrieval, backfilling event data, and one-time historical queries for DeFi protocols, NFT marketplaces, and Crypto.com ecosystem integrations.