I am trying to implement custom audits using the lighthouse library lighthouse and executing some Javascript commands within the Gatherer I get the following error:
Protocol error (Runtime.evaluate): Object reference chain is too long
In detail I have the following Gatherer:
'use strict';
const { Gatherer } = require('lighthouse');
class customGatherer extends Gatherer {
afterPass(options, loadData) {
const expression = `window.document.getElementsByTagName('*')`;
const driver = options.driver;
return driver.evaluateAsync(expression);
}
}
module.exports = customGatherer;
That with the expression defined above triggers the problem.
There seems to be too much information and I can't manage it. I'm testing the command on a web page and it returns 1059 collections (HTMLCollection(1059)).
When I run the lighthouse command to inspect a page, the warning is created and the result cannot be manipulated within the audit:
LH:Runner:warn customGatherer, required by audit my-custom-audit, encountered an error: Protocol error (Runtime.evaluate): Object reference chain is too long +0ms
NB: In the lighthouse log i can see also this error:
LH:method <= browser ERR:error Runtime.evaluate +24ms
I need to have a Gatherer that returns all HTMLCollection elements in order to compute them to get all the fonts on the page. How can I get around this problem?
There is already an artifact that collects all font information on a page: https://github.com/GoogleChrome/lighthouse/blob/master/types/artifacts.d.ts#L139
As for the actual error, you'd need to write a more complex function that you'd pass to evaluate to process the DOM and return only the data you want. If you write anything more than a single-line expression I suggest using driver.evaluate instead (see the Lighthouse repo for examples).