Collapsing and loading all files in a large pull request, from Chrome Dev Tools

collapseAll.js

//tested on GitHub 2017-03-24, this collapses all diffs including non-loaded ones
$$('.pr-2').forEach(function(element){if(element.attributes['aria-label'].value ==  "Toggle diff text") { element.click(); }});

loadAll.js

//tested on GitHub 2017-03-24, this loads all deferred diffs
$$('js-detail-target').forEach(function(element){element.click()});