hubcap metrics

Get performance metrics from the browser.

When to use

Use metrics to get a quick snapshot of performance data like JavaScript heap size, DOM node count, and layout count. This is a lightweight health check without the overhead of full profiling. Use trace for detailed performance traces or heapsnapshot for memory analysis.

Usage

hubcap metrics

Arguments

None.

Flags

None.

Output

Field	Type	Description
metrics	object	Key-value map of performance metric names to numeric values
metrics.JSHeapUsedSize	number	Bytes of JavaScript heap currently in use
metrics.JSHeapTotalSize	number	Total bytes allocated for the JavaScript heap
metrics.Nodes	number	Number of DOM nodes in the document
metrics.LayoutCount	number	Number of layout operations performed
metrics.Timestamp	number	Timestamp of the measurement

{
  "metrics": {
    "Timestamp": 1234567.89,
    "JSHeapUsedSize": 5242880,
    "JSHeapTotalSize": 8388608,
    "Nodes": 150,
    "LayoutCount": 12,
    "RecalcStyleCount": 8,
    "Documents": 1,
    "Frames": 1
  }
}

Errors

Condition	Exit code	Stderr
Chrome not connected	2	`error: connecting to Chrome: ...`
Timeout	3	`error: timeout`

Examples

Get performance metrics:

hubcap metrics

Check JS heap usage in megabytes:

hubcap metrics | jq '.metrics.JSHeapUsedSize / 1048576 | round | tostring + " MB"'

Monitor DOM node count before and after an action:

BEFORE=$(hubcap metrics | jq '.metrics.Nodes') && hubcap click "#load-more" && hubcap waitidle && AFTER=$(hubcap metrics | jq '.metrics.Nodes') && echo "Nodes added: $(( AFTER - BEFORE ))"