js: Bring debugging abilities up to the level of the browser by AtkinsSJ · Pull Request #11397 · LadybirdBrowser/ladybird

AtkinsSJ · 2026-08-27T14:34:36Z

Extends js's debugging abilities with the functionality added in #11128. The current list is:

backtrace (bt)
break (b) [file:]<line>[:column] [condition]
breakpoints
continue (c)
delete <id>
help
print (p) <expression>
set pause-on-exceptions <none|unhandled|all>
show pause-on-exceptions
step-into (step, s)
step-out (finish, fin)
step-over (next, n)

coderabbitai · 2026-08-27T14:35:38Z

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro Plus

Run ID: 7a036e99-ebd4-4bb7-aa3b-e84941060e7d

📥 Commits

Reviewing files that changed from the base of the PR and between f0cfe7d and dd13608.

📒 Files selected for processing (16)

Tests/LibJS/CMakeLists.txt
Tests/LibJS/Debugger/expected/basic.txt
Tests/LibJS/Debugger/expected/conditional-breakpoints.txt
Tests/LibJS/Debugger/expected/pause-on-exceptions.txt
Tests/LibJS/Debugger/expected/stepping.txt
Tests/LibJS/Debugger/input/basic.commands
Tests/LibJS/Debugger/input/basic.js
Tests/LibJS/Debugger/input/conditional-breakpoints.commands
Tests/LibJS/Debugger/input/conditional-breakpoints.js
Tests/LibJS/Debugger/input/pause-on-exceptions.args
Tests/LibJS/Debugger/input/pause-on-exceptions.commands
Tests/LibJS/Debugger/input/pause-on-exceptions.js
Tests/LibJS/Debugger/input/stepping.commands
Tests/LibJS/Debugger/input/stepping.js
Tests/LibJS/Debugger/output/.gitignore
Tests/LibJS/test-js-debugger.py

Included review availability: Your plan provides up to 10 included reviews per hour; 9 remain after this review.

📝 Walkthrough

Walkthrough

The debugger now supports frame evaluation without updating original bindings. The js debugger uses named commands and aliases for breakpoints, stepping, backtraces, expression printing, and pause-on-exception settings. Breakpoints can have conditions. The CLI accepts --pause-on-exceptions. C++ and Python tests cover frame evaluation, command output, stepping, exception pauses, and conditional breakpoints.

Sequence Diagram(s)

sequenceDiagram
  participant js_REPL as js debugger REPL
  participant Debugger
  participant PausedFrame
  js_REPL->>Debugger: set breakpoint and condition
  Debugger->>PausedFrame: pause at breakpoint
  js_REPL->>PausedFrame: evaluate condition
  PausedFrame-->>js_REPL: return condition result
  js_REPL->>Debugger: continue or display pause

Merge Risk: ⚪ Minimal · up to dd136

This PR adds opt-in local JavaScript debugging features without introducing a concrete merge-blocking risk; it is merge-ready after normal checks and review.

🚥 Pre-merge checks | ✅ 3

✅ Passed checks (3 passed)

Check name	Status	Explanation
Description check	✅ Passed	The description directly summarizes the new debugger commands and aliases implemented in the changeset, including breakpoints, expression evaluation, exception handling, and stepping.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

Thanks for using CodeRabbit! It's free for OSS, and your support helps us grow. If you like it, consider giving us a shout-out.

❤️ Share

_{Comment @coderabbitai help to get the list of available commands.}

Debugger input is read by a dedicated prompt and cannot be confused with JavaScript input. Use conventional command names without the unnecessary dot prefix.

Use one GenericLexer for both the command name and its arguments. Leave the cursor positioned after the name so every command continues parsing from it without command-specific substring offsets.

This exercises the debugger functionality of the `js` utility. It generally follows the same form as test-js-ast and test-js-bytecode, but we have multiple input files per test: - `input/foo.js`: The JS file to execute in the debugger. - `input/foo.commands`: The debugger commands to execute, one per line. - `input/foo.args`: An optional file with any extra command-line args to pass to the `js` binary to run this test. - `expected/foo.txt` is then the contents of stdout and stderr. The basic test added here does not use an `.args` file, but later, we'll use it to exercise the `--pause-on-exceptions` argument.

Accept c for continue and b for break. These familiar aliases reduce typing without making the full JavaScript-oriented command names less clear.

Allow debugger sessions to pause on no exceptions, unhandled exceptions, or all exceptions. Expose the policy through both a command-line option and set and show debugger commands.

Print paused execution frames from newest to oldest with function names and available source locations. Accept bt as the familiar short form.

Allow paused-frame evaluation without writing temporary local and argument binding changes back into that frame. Preserve the existing mutating behavior by default.

Add print and p commands that evaluate expressions in the current paused frame. Use non-mutating evaluation so inspection does not alter local variables or arguments.

Expose step-over, step-into, and step-out through command names that describe their behavior directly. Also accept the corresponding GDB commands and abbreviations for users familiar with them.

Accept an optional JavaScript condition after each breakpoint location and show it when listing breakpoints. Evaluate conditions in the paused frame and resume automatically when no breakpoint should stop.

AtkinsSJ · 2026-08-28T10:49:32Z

Rebased, and modified how test-js-debugger works. Each test case is now split into files like with the similar js tests:

input/foo.js: The JS file to execute in the debugger.
input/foo.commands: The debugger commands to execute, one per line.
input/foo.args: An optional file with any extra command-line args to pass to the js binary to run this test.
expected/foo.txt is then the contents of stdout and stderr.

gmta reviewed Aug 28, 2026

View reviewed changes

Comment thread Tests/LibJS/test-js-debugger.py Outdated

AtkinsSJ added 10 commits August 28, 2026 10:54

Utilities/js: Remove dots from debugger commands

d472b8a

Debugger input is read by a dedicated prompt and cannot be confused with JavaScript input. Use conventional command names without the unnecessary dot prefix.

Utilities/js: Parse debugger input with GenericLexer

b1a4960

Use one GenericLexer for both the command name and its arguments. Leave the cursor positioned after the name so every command continues parsing from it without command-specific substring offsets.

Utilities/js: Add debugger command aliases

de84b76

Accept c for continue and b for break. These familiar aliases reduce typing without making the full JavaScript-oriented command names less clear.

Utilities/js: Add exception pause controls

133c638

Allow debugger sessions to pause on no exceptions, unhandled exceptions, or all exceptions. Expose the policy through both a command-line option and set and show debugger commands.

Utilities/js: Add a debugger backtrace command

34740c4

Print paused execution frames from newest to oldest with function names and available source locations. Accept bt as the familiar short form.

LibJS: Support non-mutating debugger evaluation

3b324c6

Allow paused-frame evaluation without writing temporary local and argument binding changes back into that frame. Preserve the existing mutating behavior by default.

Utilities/js: Print paused expressions

7a44e09

Add print and p commands that evaluate expressions in the current paused frame. Use non-mutating evaluation so inspection does not alter local variables or arguments.

Utilities/js: Add debugger stepping commands

e765128

Expose step-over, step-into, and step-out through command names that describe their behavior directly. Also accept the corresponding GDB commands and abbreviations for users familiar with them.

Utilities/js: Add conditional breakpoints

dd13608

Accept an optional JavaScript condition after each breakpoint location and show it when listing breakpoints. Evaluate conditions in the paused frame and resume automatically when no breakpoint should stop.

AtkinsSJ force-pushed the extra-debugging-in-js-app branch from f0cfe7d to dd13608 Compare August 28, 2026 10:47

Navigation Menu

Uh oh!

Uh oh!

js: Bring debugging abilities up to the level of the browser - #11397

js: Bring debugging abilities up to the level of the browser#11397
AtkinsSJ wants to merge 10 commits into
LadybirdBrowser:masterfrom
AtkinsSJ:extra-debugging-in-js-app

AtkinsSJ commented Aug 27, 2026

Uh oh!

coderabbitai Bot commented Aug 27, 2026 •

edited

Loading

Walkthrough

Sequence Diagram(s)

Uh oh!

Uh oh!

AtkinsSJ commented Aug 28, 2026

Uh oh!

Reviewers

Assignees

Labels

Projects

Milestone

Development

Uh oh!

2 participants

Uh oh!

Uh oh!

Conversation

AtkinsSJ commented Aug 27, 2026

Uh oh!

coderabbitai Bot commented Aug 27, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Walkthrough

Sequence Diagram(s)

Uh oh!

Uh oh!

AtkinsSJ commented Aug 28, 2026

Uh oh!

Reviewers

Assignees

Labels

Projects

Milestone

Development

Uh oh!

2 participants

coderabbitai Bot commented Aug 27, 2026 •

edited

Loading