Tips for troubleshooting JavaScript within an embedded V8 environment

Currently, I am endeavoring to grasp the functioning of the Debug object in V8 for debugging javascript within an embedded-javascript C++ application.

After invoking v8::Debug::SetDebugEventListener and specifying a callback function, I proceed to execute v8::Debug::GetDebugContext to obtain a debug context. Following this, I typically run: Debug.scripts()

Upon printing the output of this call from within the C++ code, the resulting data is as follows:

 [{}, {}, {}, {}, {}, {}, {}, {}, {}, {}, {}, {}, {}, {}, {}, {}, {}, {}, {}, {}, {}, {}, {}, {}, {}, {}, {}, {}, {}, {}, {}, {}, {}, {}, {}, {}, {}, {}, {}, {}, {}, {}, {}, {}, {}, {}, {}, {}, {}, {}, {}, {}, {}]

My ultimate aim is to establish a breakpoint at a designated line number in a script; however, I am encountering various hurdles even with basic operations.

Despite receiving callbacks from my debug event listener, the input parameter data within these callbacks appears to be nonsensical or unclear.

{script_: {context_: {data_: undefined, handle_: 0, type_: "context"}, handle_: 1, script_: {}, type_: "script"}, type_: 4}
{break_id: 2, selected_frame: 0}

Your assistance would be greatly appreciated.

javascriptv8embedded-v8

Answer №1

(Disclaimer: The method described below may not be the optimal solution for every case, but it has proven effective in some straightforward scenarios)

v8::DebugEvent debug_event_type = event_details.GetEvent();

Next, a switch statement is used to handle the outcomes:

if (debug_event_type == v8::DebugEvent::Break) {

Provided here is an example of the data passed through when a basic breakpoint is triggered:

 /* GetEventData() when a breakpoint is hit returns:
     * {
     *      break_points_hit_: [{active_: true, actual_location: {column: 4, line: 13, script_id: 55}, condition_: null,
     *      script_break_point_: {
     *          active_: true,
     *          break_points_: [],
     *          column_: undefined,
     *          condition_: undefined,
     *          groupId_: undefined,
     *          line_: 13,
     *          number_: 1, <== breakpoint number - v8-assigned
     *          position_alignment_: 0,
     *          script_id_: 55, <== script id passed in from v8::ScriptOrigin when compiled
     *          type_: 0
 *          },
 *          source_position_: 175}], frame_: {break_id_: 8, details_: {break_id_: 8, details_: [392424216, {}, function a(){
    println("Beginning of a()");
    let some_var = 5;
    some_var += 5;
    b(some_var);
    println("End of a()");
}, {sourceColumnStart_: [undefined, undefined, undefined, undefined, undefined, undefined, undefined, undefined, undefined, undefined, undefined, undefined, undefined, 4, undefined, undefined, undefined, undefined, undefined, undefined, undefined]}, 0, 1, 175, false, false, 0, "some_var", 5]}, index_: 0, type_: "frame"}}

shameless self promotion: For further insights into my progress with V8 debugging, check out my V8 integration simplification library v8toolkit at: https://github.com/xaxxon/v8toolkit/blob/master/src/debugger.cpp

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