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The Client class is the base implementation for all JavaScript SDK clients. It handles event capture, transport, integrations, and lifecycle management.

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Overview

The Client is responsible for:
  • Capturing exceptions, messages, and events
  • Managing integrations and event processors
  • Sending data to Sentry via transports
  • Managing scope and session data

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Class Definition

export abstract class Client<O extends ClientOptions = ClientOptions> {
  protected readonly _options: O;
  protected readonly _dsn?: DsnComponents;
  protected readonly _transport?: Transport;
  protected _integrations: IntegrationIndex;
  protected _numProcessing: number;
  protected _eventProcessors: EventProcessor[];
  protected _outcomes: { [key: string]: number };
  protected _hooks: Record<string, Set<Function>>;
  protected _promiseBuffer: PromiseBuffer<unknown>;

  protected constructor(options: O);
}

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Constructor

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options
ClientOptions
required
Configuration options for the client. See Configuration Options for details.

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Methods

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captureException

Captures an exception event and sends it to Sentry. 
public captureException(
  exception: unknown,
  hint?: EventHint,
  scope?: Scope
): string
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exception
unknown
required
The exception to capture. Can be an Error object or any value.
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hint
EventHint
Additional information about the exception context.
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scope
Scope
The scope containing event metadata. If not provided, uses the current scope.
Returns: string - The event ID of the captured exception. Example: 
const client = new NodeClient(options);
const eventId = client.captureException(new Error('Something went wrong'), {
  originalException: error,
  data: { userId: '123' }
}, scope);

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captureMessage

Captures a message event and sends it to Sentry. 
public captureMessage(
  message: ParameterizedString,
  level?: SeverityLevel,
  hint?: EventHint,
  currentScope?: Scope
): string
​
message
ParameterizedString | string
required
The message to capture.
​
level
SeverityLevel
The severity level: 'fatal', 'error', 'warning', 'info', or 'debug'.
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hint
EventHint
Additional information about the message context.
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currentScope
Scope
The scope containing event metadata.
Returns: string - The event ID of the captured message. Example: 
const eventId = client.captureMessage(
  'User login failed',
  'warning',
  { data: { username: 'john' } }
);

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captureEvent

Captures a manually created event and sends it to Sentry. 
public captureEvent(
  event: Event,
  hint?: EventHint,
  currentScope?: Scope
): string
​
event
Event
required
The event object to send. See Event Types for structure.
​
hint
EventHint
Additional metadata about the event.
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currentScope
Scope
The scope containing event metadata.
Returns: string - The event ID.

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flush

Wait for all events to be sent or the timeout to expire. 
public async flush(timeout?: number): Promise<boolean>
​
timeout
number
Maximum time in milliseconds to wait. Omitting this will wait until all events are sent.
Returns: Promise<boolean> - true if all events are sent before timeout, false otherwise. Example: 
// Flush with 5 second timeout
const success = await client.flush(5000);
if (!success) {
  console.warn('Some events were not sent');
}

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close

Flush the event queue and disable the client. 
public async close(timeout?: number): Promise<boolean>
​
timeout
number
Maximum time in milliseconds to wait before shutting down.
Returns: Promise<boolean> - true if flush completes successfully, false otherwise. Example: 
// Clean shutdown
await client.close(2000);

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getDsn

Get the current DSN. 
public getDsn(): DsnComponents | undefined
Returns: The parsed DSN components or undefined if no DSN is configured.

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getOptions

Get the client options. 
public getOptions(): O
Returns: The options passed to the client constructor.

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getTransport

Get the transport used by the client. 
public getTransport(): Transport | undefined
Returns: The transport instance or undefined if not initialized.

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addIntegration

Add an integration to the client at runtime. 
public addIntegration(integration: Integration): void
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integration
Integration
required
The integration to add.
Example: 
import { httpIntegration } from '@sentry/node';

client.addIntegration(httpIntegration());

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getIntegrationByName

Get an installed integration by name. 
public getIntegrationByName<T extends Integration = Integration>(
  integrationName: string
): T | undefined
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integrationName
string
required
The name of the integration.
Returns: The integration instance or undefined.

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addEventProcessor

Add an event processor that applies to all events. 
public addEventProcessor(eventProcessor: EventProcessor): void
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eventProcessor
EventProcessor
required
A function that processes events before they are sent.
Example: 
client.addEventProcessor((event, hint) => {
  // Modify event before sending
  event.tags = { ...event.tags, processed: 'true' };
  return event;
});

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on

Register a callback for lifecycle hooks. 
public on(
  hook: 'spanStart' | 'spanEnd' | 'beforeSendEvent' | 'flush' | ...,
  callback: Function
): () => void
Returns: A function that removes the registered callback. Example: 
const unsubscribe = client.on('spanStart', (span) => {
  console.log('Span started:', span.spanContext().spanId);
});

// Later, remove the callback
unsubscribe();

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emit

Emit a hook event. 
public emit(hook: string, ...args: unknown[]): void

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Hooks

The Client supports various lifecycle hooks:
  • spanStart - Fired when a span starts
  • spanEnd - Fired when a span ends
  • beforeSendEvent - Fired before sending an event
  • afterSendEvent - Fired after sending an event
  • beforeAddBreadcrumb - Fired before adding a breadcrumb
  • flush - Fired when flushing
  • close - Fired when closing