FiddlerScriptSnippet.js

/// should be inside 
/// static function OnBeforeRequest(oSession: Session) { ... }


if ( true/*some condition*/ ) {
 
    var fso = new ActiveXObject("Scripting.FileSystemObject"),
        fl = fso.OpenTextFile("c:\\path\\mocks\\manifest.json", 1),
        content = fl.ReadAll(),
        mockCalls,
        mockCallsLen,
        mockType = 'a',
        i;

    eval("content = " + content + ";");

    mockCalls = content[mockType];
    mockCallsLen = mockCalls.length;

    for (i = 0; i < mockCallsLen; i += 1) {
        if ( oSession.fullUrl.Contains(mockCalls[i]) ) {
            oSession["ui-backcolor"] = "lime";
            oSession["ui-bold"] = "changing URL for this session";
            oSession.fullUrl = oSession.fullUrl.Replace('service', 'mocks/' + mockType);
        }
    }
}

gen.js

/*jshint node:true*/
'use strict';
var
	fs = require('fs'),
	fsroot = './mocks',
	manifest = {};

function writeManifest(manifest) {
	manifest = JSON.stringify(manifest);
	fs.writeFileSync(fsroot + '/manifest.json', manifest);
	console.log('completed!');
}

function readRequests(root, variant) {
	var
		requests = fs.readdirSync(fsroot + '/' + variant + '/' + root),
		len = requests.length;

	for (;len--;) {
		manifest[variant].push(root + '/' + requests[len]);
	}
}

function readRoots(variants) {
	var
		len = variants.length,
		roots,
		rlen,
		it;

	for (;len--;) {

		it = variants[len];
		roots = fs.readdirSync(it.target);
		rlen = roots.length;
		manifest[it.variant] = [];

		for (;rlen--;) {

			readRequests(roots[rlen], it.variant);
		}

	}

	writeManifest(manifest);
}

function readVariants(err, files) {
	var
		variants = [],
		len,
		target;

	if (!err) {

		len = files.length;

		for (;len--;) {
			target = fsroot + '/' + files[len];
			if ( fs.existsSync(target) && fs.statSync(target).isDirectory() ) {
				if ( files[len] !== 'script' ) {

					variants.push({'target': target, 'variant': files[len]});
				}
			}

		}

		readRoots(variants);
	} else {

		throw(err);
	}

}


fs.readdir(fsroot, readVariants);