Fix to #1627

[NoamPaz]

Fix issue #1627 by creating an error object and use the property 'stack' only when needed, instead of read stack property in the creation time of the error object.

Background (Problem in detail)

The slowness seems to come from accessing the .stack property on the error, as v8 seems to go through considerable trouble in order to convert it from its internal representation to the string version it uses to report errors.

Solution

the fix for this is to change the line to method.stackTraceError = new Error("Stack Trace for original"), and only access the .stack property if an error needs to be reported.

####Test
passed: 'npm run test' and 'npm run lint'

[mroderick]

Thank you for taking the time to investigate this issue and making a pull request 🚀

Your example script in the gist doesn't exercise actual Sinon code. I wanted to make sure that there would be an improvement for an example that exercises Sinon.

So, I created a little benchmark script using Benchmark.js.

"use strict";

var Benchmark = require("benchmark");
var suite = new Benchmark.Suite();
var sinon = require("./lib/sinon");
var sandbox = sinon.createSandbox();

// add tests
suite.add("stub test", function () {
    var obj = {
        hello: function hello() {
            return "world";
        }
    };

    sandbox.stub(obj, "hello");
});
// add listeners
suite.on("cycle", function (event) {
    console.log(String(event.target));
});
suite.on("complete", function () {
    console.log("Fastest is " + this.filter("fastest").map("name"));
});
// run async
suite.run({
    "async": true
});

When run against current master 5063c33, these are the results on my ageing laptop:

stub test x 4,852 ops/sec ±3.78% (59 runs sampled)

Run against this branch:

stub test x 10,129 ops/sec ±3.17% (64 runs sampled)

The benchmarks show a pretty significant speedup!

Excellent pull request 👍

[mroderick]

This has been published as sinon@4.2.1