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rewrites JavaScript code to collect partial execution traces


Collect real-time JavaScript traces (number of times a function has been called, locations where exceptions have been thrown, etc).

Easily instrument an entire program with node-theseus.

Plain objects are returned from all API calls so that they can be passed around as JSON. node-theseus does this with a WebSocket. Theseus does it over Chrome's Remote Debugging API (which boils down to a WebSocket).

npm install fondue

Execute instrumented code:

var fondue = require('fondue'),
    vm = require('vm');
var src = fondue.instrument('function foo(a) { return a * 2 }; foo(4)');
var sandbox = { __tracer: undefined };
var output = vm.runInNewContext(src, sandbox);
var tracer = sandbox.__tracer; // created by fondue when instrumented code is run 

Track trace points (functions, call sites, etc):

var functions = {};
var nodesHandle = tracer.trackNodes();
tracer.newNodes(nodesHandle).forEach(function (n) {
    if (n.type === 'function') {
        functions[] = n;
var fooNode = functions['foo'];
console.log('foo started at', fooNode.start, 'and ended at', fooNode.end);
// call tracer.newNodes() periodically if you expect new code to be required over time 

Track hit counts:

// check how many times trace points have been hit 
var hitsHandle = tracer.trackHits();
var hits1 = tracer.hitCountDeltas(hitsHandle);
console.log('foo was called ' + (hits1[] || 0) + ' time');
// call repeatedly to track hit counts over time 
var hits2 = tracer.hitCountDeltas(hitsHandle);
console.log('foo was called ' + (hits2[] || 0) + ' times (since last check)');

Access function arguments and return values (and unhandled exceptions):

var logHandle = tracer.trackLogs({ ids: [] });
var invocations = tracer.logDelta(logHandle);
console.log('foo returned:', invocations[0].returnValue);
console.log('foo accepted arguments:', invocations[0].arguments);