v0.1.11811 Aug 2026·JavaScript & JIT, DevTools, Tabs & interface

DevTools debugger: step over, into and out

A breakpoint stops being a snapshot and becomes a place you can walk from. Turn on Pause & step, set a line breakpoint, reload - and when execution stops the engine genuinely SUSPENDS, so Step Over, Step Into and Step Out move it one source line at a time, with the live scope updating at every stop. Step Over runs a function call on the current line to completion and lands on the next line; Step Into descends into that call; Step Out runs to the end of the current function and stops back in its caller. This is the feature that turns a set of breakpoints into an actual debugger. It is off by default, so a page that is not being debugged runs exactly as before and the whole conformance suite is unchanged. DevTools moves 28 to 31; overall holds at 51.

Parity with the reference browser

74overall, as of v0.1.343

Web APIs / DOM surface42

Security architecture66

GPU / graphics acceleration68

DevTools / extensions72

Networking85

Media85

Accessibility85

Real-world site compatibility99

HTML parsing100

CSS parsing + selectors100

Layout: block / flex / grid / tables / writing-modes100

Paint + visual100

JavaScript language100

JavaScript performance (JIT)100

HTML parsing100

What changed 3 changes

JavaScript & JIT	Step over / into / out with correct call-depth semantics: a step runs to the next source-line boundary whose call depth satisfies the step (over = same-or-shallower frame so a call runs whole, into = any depth so it descends, out = a shallower frame so it returns to the caller), using a composite depth that stays monotonic across both the in-loop call path and native higher-order-function callbacks. Verified against the full (reason, line, function, depth) trace: two step-overs walk lines 5 -> 6 -> 7 without ever entering the function called on line 6, and step-into then step-out reach the callee and return.
JavaScript & JIT	A true interactive suspend, not a simulation: with stepping on, a breakpoint BLOCKS the engine thread until you step or resume (a gate test spins up the engine on its own thread, asserts it has actually blocked, then signals a step and watches it wake to completion). Because the engine thread is blocked while paused, the step/resume command is delivered out-of-band through a process-global gate rather than the normal message loop, with a 30-second safety timeout so a page can never hang. Off by default and zero-cost when off, so the conformance gate is unchanged at 6375/6375 (native-JIT and no-nanbox green).
Tabs & interface	Wired end to end: a Pause & step toggle plus Over / Into / Out / Resume controls in the visual Debugger panel, backed by CDP Debugger.stepOver / stepInto / stepOut and a __debug_step native. This is the keystone of the v0.1.112-118 debugger arc (breakpoints, pause-on-exceptions, evaluate-at-breakpoint, source-line breakpoints, and now stepping); a Sources gutter and a WebSocket transport for external tooling are the remaining pieces. Research note in docs/devtools-stepping.md.