Performance Metrics — Page Timing via CDP

Foxbridge implements Performance.getMetrics by evaluating performance.timing in the page context, returning real browser timing data.

Usage


const client = await page.createCDPSession();
await client.send('Performance.enable');
const { metrics } = await client.send('Performance.getMetrics');
 
for (const { name, value } of metrics) {
  console.log(`${name}: ${value}`);
}

Returned Metrics

Metric	Source	Description
`Timestamp`	`Date.now() / 1000`	Current time in seconds
`Documents`	`document.querySelectorAll('*').length`	Total DOM element count
`Frames`	`window.frames.length`	Number of frames
`JSEventListeners`	Constant `0`	Not available in Firefox
`DomContentLoaded`	`performance.timing`	Time to DOMContentLoaded (seconds)
`NavigationStart`	`performance.timing`	Navigation start timestamp
`DomInteractive`	`performance.timing`	Time to DOM interactive (seconds)
`FirstMeaningfulPaint`	`performance.timing.responseEnd`	Approximated from response end
`TaskDuration`	`performance.now() / 1000`	Page uptime in seconds
`JSHeapUsedSize`	`performance.memory`	Used JS heap (if available)
`JSHeapTotalSize`	`performance.memory`	Total JS heap (if available)

Timing-based metrics (DomContentLoaded, NavigationStart, DomInteractive, FirstMeaningfulPaint) are only included when the corresponding performance.timing values are non-zero.

Implementation

The metrics are collected via a single Runtime.evaluate call injected into the page. This avoids any protocol-level dependency on Chrome-specific performance APIs.

If evaluation fails (e.g., the page has no content), a fallback response with just Timestamp: 0 is returned.

Protocol Methods

Method	Behavior
`Performance.enable`	No-op (always available)
`Performance.disable`	No-op
`Performance.getMetrics`	Evaluates JS and returns metrics array

Performance Metrics — Page Timing via CDP

Usage

Returned Metrics

Implementation

Protocol Methods

See also