Class: Tracer

lib/core/trace/tracer~Tracer()

The active tracer.

A singleton rather than a per-app instance: the reactive system, the sandbox and the patcher are all module-scoped, so a per-app tracer would need threading through call sites that have no app reference. Recording more than one application at a time is not a use case V1 supports.

Constructor

new Tracer()

Constructs the inactive tracer installed at import time.

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Members

on :boolean

Hot-path flag. Read by every instrumented site in the runtime, so it is a plain own property rather than a getter.

Type:
  • boolean
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sink :object|null

The recorder receiving nodes, or null when tracing is off.

Type:
  • object | null
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stack :Array:.<number:>

Ids of the nodes currently executing, innermost last.

Type:
  • Array:.<number:>
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Methods

annotate(fields)

Attaches a field to the node most recently entered.

Used where the interesting value is only known once the node's body has run — a computed's new value, an action's return, a resource's outcome.

Parameters:
Name Type Description
fields object

Fields to merge into the open node.
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attach(sink) → {Tracer}

Begins recording into a sink.

Parameters:
Name Type Description
sink object

The recorder to feed.
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Returns:

This tracer.

Type
Tracer

continueFrom(id) → {number}

Re-enters an existing node's causal scope without recording a new node.

The scheduler batches component updates into a microtask, so the DOM patch caused by a click happens on an empty causal stack — long after the click handler returned. Stamping the queued job with the node that queued it and resuming that scope here is what keeps a patch attributed to the write that caused it, rather than appearing as an unexplained root.

Parameters:
Name Type Description
id number | null

The node id to continue from.
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Returns:

A restore token for leave, or -1 when tracing is off.

Type
number

current() → {number|null}

The id of the node currently being executed, or null at the top level.

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Returns:

The causal parent for anything emitted right now.

Type
number | null

detach() → {object|null}

Stops recording and drops the sink.

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Returns:

The detached recorder.

Type
object | null

enter(type, data) → {number}

Records a node and makes it the causal parent of everything emitted until the matching Tracer#leave.

Parameters:
Name Type Description
type string

A TraceNodeType.
data object

Type-specific fields.
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Returns:

A restore token to hand to leave, or -1 when tracing is off.

Type
number

leave(token)

Restores the causal stack to the depth a matching enter returned.

Parameters:
Name Type Description
token number

The token from enter.
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markNonDeterministic(reason, detailopt)

Reports that something happened which replay cannot reproduce.

Parameters:
Name Type Attributes Description
reason string

A non-determinism reason.
detail string <optional>

Extra context shown to the developer.
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record(type, data) → {object|null}

Records a leaf node — something that happened, but that nothing else happened inside.

Parameters:
Name Type Description
type string

A TraceNodeType.
data object

Type-specific fields.
Source:
Returns:

The stored node, or null when tracing is off.

Type
object | null

recordError(error, contextopt) → {object|null}

Records an error that escaped application code.

Parameters:
Name Type Attributes Description
error Error

The error.
context object <optional>

Where it came from.
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Returns:

The stored node.

Type
object | null