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events

Subscribes to Flow blockchain events in real-time. This function provides a way to listen for specific events emitted by smart contracts on the Flow blockchain. It automatically handles fallback to legacy polling for environments that don't support WebSocket subscriptions.

Import​

You can import the entire package and access the function:


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import * as fcl from "@onflow/fcl"
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fcl.events(filterOrType)

Or import directly the specific function:


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import { events } from "@onflow/fcl"
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events(filterOrType)

Usage​


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// Subscribe to a specific event type
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import * as fcl from "@onflow/fcl"
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const unsubscribe = fcl.events("A.0x1654653399040a61.FlowToken.TokensWithdrawn")
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.subscribe((event) => {
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console.log("Event received:", event)
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console.log("Event data:", event.data)
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console.log("Transaction ID:", event.transactionId)
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})
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// Stop listening after 30 seconds
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setTimeout(() => {
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unsubscribe()
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}, 30000)
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// Subscribe to multiple event types with error handling
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const unsubscribe = fcl.events({
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eventTypes: [
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"A.0x1654653399040a61.FlowToken.TokensWithdrawn",
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"A.0x1654653399040a61.FlowToken.TokensDeposited"
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]
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}).subscribe(
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(event) => {
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console.log("Token event:", event.type, event.data)
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},
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(error) => {
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console.error("Event subscription error:", error)
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}
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)
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// Subscribe to events starting from a specific block height
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const unsubscribe = fcl.events({
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eventTypes: ["A.CONTRACT.EVENT"],
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startBlockHeight: 12345678
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}).subscribe((event) => {
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console.log("Historical and new events:", event)
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})

Parameters​

filterOrType (optional)​

  • Type: string | EventFilter
  • Description: Event filter object or event type string. If a string is provided, it will be treated as a single event type to subscribe to. If an EventFilter object is provided, it can contain multiple event types and other filter criteria.

Properties:​

  • eventTypes - Array of event type strings to subscribe to
  • startBlockId - Block ID to start streaming from
  • startBlockHeight - Block height to start streaming from

Returns​


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{
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subscribe: (onData: (event: Event) => void, onError?: (error: Error) => void) => () => void;
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}

An object containing a subscribe method • returns.subscribe Function to start the subscription • returns.subscribe.onData Callback function called when an event is received • returns.subscribe.onError Optional callback function called when an error occurs • returns.subscribe.unsubscribe Function returned by subscribe() to stop the subscription

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