perf(exhaustMap): remove tryCatch/errorObject (~10% improvement)

[luisgabriel]

Before:

                       |     RxJS 4.0.7 | RxJS 5.0.0-beta.1 | factor | % improved
----------------------------------------------------------------------------------
exhaustMap - immediate | 1,449 (±0.95%) |   17,023 (±0.88%) | 11.75x |   1,075.1%
            exhaustMap | 4,732 (±0.34%) |   80,795 (±0.38%) | 17.07x |   1,607.4%

After:

                       |     RxJS 4.0.7 | RxJS 5.0.0-beta.1 | factor | % improved
----------------------------------------------------------------------------------
exhaustMap - immediate | 1,452 (±1.14%) |   18,523 (±0.68%) | 12.76x |   1,175.5%
            exhaustMap | 4,941 (±0.29%) |   87,146 (±0.39%) | 17.64x |   1,663.8%

[kwonoj]

Change looks good to me.

[david-driscoll]

I have a (potentially dumb question) will these change affect the flame graph in any way? Or is the errorObject just a hold over from RxJS4?

[kwonoj]

I assume there won't be much changes, custom trycatcher is simply wraps trycatch by

function tryCatcher(): any {
  try {
    return tryCatchTarget.apply(this, arguments);
  } catch (e) {
    errorObject.e = e;
    return errorObject;
  }
}

call stack may look slightly difference by catching internally.

[kwonoj]

just curious @david-driscoll , any particular concern you have in mind?

[david-driscoll]

nope, just curious if it was related to handling the flamegraphs at all. I know in the past the common error object was used for creating custom callback chains (I think, but it's been a while).

[kwonoj]

This PR #1251 does have background explanations of reason to adapt these changes. Mainly about perf reasons.

[kwonoj]

Merged with a55f459, thanks @luisgabriel .

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