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The Tracer object

AppSignal for Node.js contains a new concept that is different to the current Ruby implementation - the Tracer object. The Tracer object contains various methods that you might use when creating your own custom instrumentation.

The Tracer is responsible for tracking the currently active Span, and exposes functions for creating and activating new Spans.

Retrieving the Tracer

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const tracer = appsignal.tracer();

If the agent is currently inactive (you must actively set it as such by setting active: true), then the AppSignal client will return an instance of NoopTracer, which is safe to call within your code as if the agent were currently active, but does not record any data.

Retrieving the current Span

In most cases, a Span will be created by one of our automatic instrumentations, e.g. the http module integration. In order to add any custom instrumentation to your trace, you'll need to retrieve that Span using the Tracer instance.

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const span = tracer.currentSpan();

Once you have the current Span, you'll be able to add data to it and create ChildSpans from it. If a current Span is not available, then tracer.currentSpan() will return a NoopSpan.

Creating a new Span

A Span can be created by calling tracer.createSpan(), which initializes a new Span object.

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const span = tracer.createSpan();

A ChildSpan, a Span that is the child of another Span, can also be created by passing an optional second argument to tracer.createSpan().

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const childSpan = tracer.createSpan(undefined, span);

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