We noticed that debugging tests in the TypeScript repo has become extremely slow after v13.2. The file we are stepping through is extremely large, which is probably part of it. Here are steps to reproduce: - Clone and build https://github.com/microsoft/TypeScript - Run `node --inspect-brk node_modules/mocha/bin/_mocha -u bdd --no-timeouts --colors built/local/run.js -f tests/cases/compiler --skip-percent 0` - Attach with devtools - Hit a breakpoint anywhere in parser.ts - Step - Notice that every step takes several seconds to pause on the next line - Using any version of node before 13.2, stepping is very fast For slightly easier setup, you can debug in VS Code with the "Mocha Tests" launch config