This is a branch of ChakraCore to support work on adding Time-Travel Debugging functionality to the Chakra JavaScript engine. The time-travel functionality adds reverse variations of the usual step forward operations provided by a debugger allowing a developer to rewind time to see the exact sequence of statements and program values leading to an error instead of going through the iterative process of re-setting breakpoints and reproducing the bug to narrow in on the source of the error.

The technique used to implement the time-travel functionality is described in an OOPSLA 2014 paper and is based on a record/replay with state snapshots design. The current code contains snapshot/restore code for the JavaScript program state, code for record/replay of events from the JsRT host, and new JsRT debugger API's that support time-travel debugging operations. Work is ongoing to complete the snapshot/inflate code and the addition of record/replay hooks to the JsRT API.

A demo video of an earlier experimental prototype of the the idea running with Node.js can be seen in the OSS announcement video. You can stay up-to-date on progress by following the MSEdge developer blog or @ChakraCore on Twitter.

You can build ChakraCore on Windows 7 SP1 or above with either Visual Studio 2013 or 2015 with C++ support installed. Once you have Visual Studio installed:

• Clone ChakraCore through git clone https://github.com/Microsoft/ChakraCore.git and switch to the TimeTravelDebugging branch
• Open Build\Chakra.Core.sln in Visual Studio
• Build Solution (x86 with debug or test configurations)

More details in Building ChakraCore.

At this point you can experiment with basic time-travel functionality in TTD ChakraCore by using the ch.exe binary. This app is a lightweight hosting of JsRT where you can run small applications. After building, you can find this binary in: Build\VcBuild\bin\[platform+output] (eg. Build\VcBuild\bin\x86_debug). Using the ch.exe application you can record the execution of a program execution using the command ch.exe -TTRecord:[logDirectoryPath] yourSrc.js (or use -TTRecord:!default for a temp default location). To time-travel debug this execution you can launch ch.exe with the command line flag ch.exe -TTDebug:[logDirectoryPath] (or -TTDebug:!default for the temp default location) which starts the time-travel execution and launches a simple command line debugger to experiemnt with. You can find more usage examples in the unit-test directory test\TTBasic\, test\TTExecuteBasic\, and test\TTDebuggerBasic\.

• OOPSLA 2014 research paper
• ChakraCore Architecture
• Contribution guidelines
• Blogs, talks and other resources

Contributions to ChakraCore TTD (and ChakraCore) are welcome. Here is how you can contribute:

• Submit pull requests to help complete TTD implementation or add new features
• Submit bugs to ChakraCore and help verify fixes
• Chat about @ChakraCore on Twitter

Please refer to Contribution guidelines for more details.

As this work started as an academic research project in the RiSE group at Microsoft Research we are also excited to support continued research and experimentation based on TTD ChakraCore code.

For details on our planned features and future direction please refer to our roadmap.

For questions about ChakraCore, please open an issue and prefix the issue title with [Question].