another silly example of using v8's in-process debugger APIs

debug-when-do.js

#!/usr/bin/env node

// run with `node --expose-debug-as=Debug fileName.js`

//------------------------------------------------------------------------------
// When the function f1 returns true, run function f2.  
// f1 will be invoked at every debug step point.
//------------------------------------------------------------------------------
function whenDo(f1, f2) {

    //--------------------------------------------------------------------------

    function dummyFunc() {}

    //--------------------------------------------------------------------------

    function listener(event, execState, eventData, data) {
        if (event != debug.DebugEvent.Break) return

        try {
            var result = f1()
            if (result) f2()
        }
        catch (e) {}

        execState.prepareStep(debug.StepAction.StepIn)
    }

    var debug = Debug.Debug

    debug.setListener(listener)
    debug.setBreakPoint(dummyFunc, 0, 0)
    dummyFunc()
}

//------------------------------------------------------------------------------

var i

whenDo(
    function(){ return i>=3 && i<=5 }, 
    function(){ console.log("i is between 3 and 5!")}
)

for (var i=0; i<10; i++) {
    console.log(i)
}