The coverage method checks the coverage info for a particular resource (JS or CSS). In order to collect coverage, you must call goto with a second parameter of { coverage: true }. This is so that Navalia can properly instrument Chrome to collect coverage.

This async method will return an object with these properties:

• total The total bytes of the script.
• unused The total unused bytes.
• percentUnused A floating-point number representing the percentage unused.

It’s likely that the Chrome browsers’s Coverage tab will report different percent numbers than Navalia. This is largely due to when you collect coverage information as more interactions on a page will return lower percentage of unused code. If you see wildly different percentages please file an issue.

JavaScript

const { Chrome } = require('navalia');
const chrome = new Chrome();

chrome.goto('http://joelgriffith.net/', { coverage: true })
.then(() => chrome.coverage('http://joelgriffith.net/main.bundle.js'))
.then((stats) => console.log(stats)) // Prints { total: 45913, unused: 5572, percentUnused: 0.12135996340905626 }
.then(() => chrome.done());

TypeScript

import { Chrome } from 'navalia';
const chrome = new Chrome();

async function checkCoverage() {
  await chrome.goto('http://joelgriffith.net/', { coverage: true });
  const stats = await chrome.coverage('http://joelgriffith.net/main.bundle.js');
  console.log(stats); // Prints { total: 45913, unused: 5572, percentUnused: 0.12135996340905626 }
  chrome.done();
}

checkCoverage();