Javascript profiling mystery - closure variables -

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i testing performance (with chrome timeline) on cases if variable defined inside closure. it's values not exposed user.

as expected run_proto_fn run few times faster , minimal garbage collections, , low memory heap.

but run_proto_obj happened make exact opposite, if costly having non-function values @ object prototype property properties.

can share clarity here? 

some = function(){};  some.prototype.exe = function(v){  	var x = {  		a:'lorem ipsum dolor sit amet, consectetur adipisicing elit. ea, quae repudiandae eveniet cumque consequatur vitae aut. nisi perspiciatis magnam explicabo optio reprehenderit dignissimos @ porro quam, neque dolorum, architecto odit?lorem ipsum dolor sit amet, consectetur adipisicing elit. ea, quae repudiandae eveniet cumque consequatur vitae aut. nisi perspiciatis magnam explicabo optio reprehenderit dignissimos @ porro quam, neque dolorum, architecto odit?lorem ipsum dolor sit amet, consectetur adipisicing elit. ea, quae repudiandae eveniet cumque consequatur vitae aut. nisi perspiciatis magnam explicabo optio reprehenderit dignissimos @ porro quam, neque dolorum, architecto odit?lorem ipsum dolor sit amet, consectetur adipisicing elit. ea, quae repudiandae eveniet cumque consequatur vitae aut. nisi perspiciatis magnam explicabo optio reprehenderit dignissimos @ porro quam, neque dolorum, architecto odit?lorem ipsum dolor sit amet, consectetur adipisicing elit. ea, quae repudiandae eveniet cumque consequatur vitae aut. nisi perspiciatis magnam explicabo optio reprehenderit dignissimos @ porro quam, neque dolorum, architecto odit?',  		b:'lorem ipsum dolor sit amet, consectetur adipisicing elit. ea, quae repudiandae eveniet cumque consequatur vitae aut. nisi perspiciatis magnam explicabo optio reprehenderit dignissimos @ porro quam, neque dolorum, architecto odit?lorem ipsum dolor sit amet, consectetur adipisicing elit. ea, quae repudiandae eveniet cumque consequatur vitae aut. nisi perspiciatis magnam explicabo optio reprehenderit dignissimos @ porro quam, neque dolorum, architecto odit?lorem ipsum dolor sit amet, consectetur adipisicing elit. ea, quae repudiandae eveniet cumque consequatur vitae aut. nisi perspiciatis magnam explicabo optio reprehenderit dignissimos @ porro quam, neque dolorum, architecto odit?lorem ipsum dolor sit amet, consectetur adipisicing elit. ea, quae repudiandae eveniet cumque consequatur vitae aut. nisi perspiciatis magnam explicabo optio reprehenderit dignissimos @ porro quam, neque dolorum, architecto odit?lorem ipsum dolor sit amet, consectetur adipisicing elit. ea, quae repudiandae eveniet cumque consequatur vitae aut. nisi perspiciatis magnam explicabo optio reprehenderit dignissimos @ porro quam, neque dolorum, architecto odit?',  		c:'lorem ipsum dolor sit amet, consectetur adipisicing elit. ea, quae repudiandae eveniet cumque consequatur vitae aut. nisi perspiciatis magnam explicabo optio reprehenderit dignissimos @ porro quam, neque dolorum, architecto odit?lorem ipsum dolor sit amet, consectetur adipisicing elit. ea, quae repudiandae eveniet cumque consequatur vitae aut. nisi perspiciatis magnam explicabo optio reprehenderit dignissimos @ porro quam, neque dolorum, architecto odit?lorem ipsum dolor sit amet, consectetur adipisicing elit. ea, quae repudiandae eveniet cumque consequatur vitae aut. nisi perspiciatis magnam explicabo optio reprehenderit dignissimos @ porro quam, neque dolorum, architecto odit?lorem ipsum dolor sit amet, consectetur adipisicing elit. ea, quae repudiandae eveniet cumque consequatur vitae aut. nisi perspiciatis magnam explicabo optio reprehenderit dignissimos @ porro quam, neque dolorum, architecto odit?lorem ipsum dolor sit amet, consectetur adipisicing elit. ea, quae repudiandae eveniet cumque consequatur vitae aut. nisi perspiciatis magnam explicabo optio reprehenderit dignissimos @ porro quam, neque dolorum, architecto odit?',  	};  	return x[v];  };    some2 = function(){};  some2.prototype.exe = function(v){  	return this.exes[v];  };  some2.prototype.exes = {  	a:'lorem ipsum dolor sit amet, consectetur adipisicing elit. ea, quae repudiandae eveniet cumque consequatur vitae aut. nisi perspiciatis magnam explicabo optio reprehenderit dignissimos @ porro quam, neque dolorum, architecto odit?lorem ipsum dolor sit amet, consectetur adipisicing elit. ea, quae repudiandae eveniet cumque consequatur vitae aut. nisi perspiciatis magnam explicabo optio reprehenderit dignissimos @ porro quam, neque dolorum, architecto odit?lorem ipsum dolor sit amet, consectetur adipisicing elit. ea, quae repudiandae eveniet cumque consequatur vitae aut. nisi perspiciatis magnam explicabo optio reprehenderit dignissimos @ porro quam, neque dolorum, architecto odit?lorem ipsum dolor sit amet, consectetur adipisicing elit. ea, quae repudiandae eveniet cumque consequatur vitae aut. nisi perspiciatis magnam explicabo optio reprehenderit dignissimos @ porro quam, neque dolorum, architecto odit?lorem ipsum dolor sit amet, consectetur adipisicing elit. ea, quae repudiandae eveniet cumque consequatur vitae aut. nisi perspiciatis magnam explicabo optio reprehenderit dignissimos @ porro quam, neque dolorum, architecto odit?',  	b:'lorem ipsum dolor sit amet, consectetur adipisicing elit. ea, quae repudiandae eveniet cumque consequatur vitae aut. nisi perspiciatis magnam explicabo optio reprehenderit dignissimos @ porro quam, neque dolorum, architecto odit?lorem ipsum dolor sit amet, consectetur adipisicing elit. ea, quae repudiandae eveniet cumque consequatur vitae aut. nisi perspiciatis magnam explicabo optio reprehenderit dignissimos @ porro quam, neque dolorum, architecto odit?lorem ipsum dolor sit amet, consectetur adipisicing elit. ea, quae repudiandae eveniet cumque consequatur vitae aut. nisi perspiciatis magnam explicabo optio reprehenderit dignissimos @ porro quam, neque dolorum, architecto odit?lorem ipsum dolor sit amet, consectetur adipisicing elit. ea, quae repudiandae eveniet cumque consequatur vitae aut. nisi perspiciatis magnam explicabo optio reprehenderit dignissimos @ porro quam, neque dolorum, architecto odit?lorem ipsum dolor sit amet, consectetur adipisicing elit. ea, quae repudiandae eveniet cumque consequatur vitae aut. nisi perspiciatis magnam explicabo optio reprehenderit dignissimos @ porro quam, neque dolorum, architecto odit?',  	c:'lorem ipsum dolor sit amet, consectetur adipisicing elit. ea, quae repudiandae eveniet cumque consequatur vitae aut. nisi perspiciatis magnam explicabo optio reprehenderit dignissimos @ porro quam, neque dolorum, architecto odit?lorem ipsum dolor sit amet, consectetur adipisicing elit. ea, quae repudiandae eveniet cumque consequatur vitae aut. nisi perspiciatis magnam explicabo optio reprehenderit dignissimos @ porro quam, neque dolorum, architecto odit?lorem ipsum dolor sit amet, consectetur adipisicing elit. ea, quae repudiandae eveniet cumque consequatur vitae aut. nisi perspiciatis magnam explicabo optio reprehenderit dignissimos @ porro quam, neque dolorum, architecto odit?lorem ipsum dolor sit amet, consectetur adipisicing elit. ea, quae repudiandae eveniet cumque consequatur vitae aut. nisi perspiciatis magnam explicabo optio reprehenderit dignissimos @ porro quam, neque dolorum, architecto odit?lorem ipsum dolor sit amet, consectetur adipisicing elit. ea, quae repudiandae eveniet cumque consequatur vitae aut. nisi perspiciatis magnam explicabo optio reprehenderit dignissimos @ porro quam, neque dolorum, architecto odit?',  };  some_fn = function(){};  some_fn.prototype.exe = function(v){  	var x = {  		a: function(p){this.p1 = p;return this;},          b:function(p){this.p2 = p*3;return this;},          c:function(p){this.p3 = p*99;return this;},      };    return x[v].call(this,42);  };    some_fn2 = function(){};  some_fn2.prototype.exe = function(v){      return this.exes[v].call(this,42);	  };  some_fn2.prototype.exes = {      a: function(p){this.p1 = p;return this;},      b:function(p){this.p2 = p*3;return this;},      c:function(p){this.p3 = p*99;return this;},  };    var a1 = a2 = a_fn1 = a_fn2 = [];  	    var run_local_obj = function(){  	for (var = 1000000 - 1; >= 0; i--) {  		x1 = new some();  		x1.exe('a');  		a1.push(x1);  	}  };  var run_proto_obj = function(){  	for (var = 1000000 - 1; >= 0; i--) {  		x2 = new some2();  		x2.exe('a');  		a2.push(x2);  	}  };  var run_local_fn = function(){  	for (var = 1000000 - 1; >= 0; i--) {  		x1 = new some_fn();  		x1.exe('a');  		x1.exe('b');  		x1.exe('c');  		a_fn1.push(x1);  	}  };  var run_proto_fn = function(){  	for (var = 1000000 - 1; >= 0; i--) {  		x2 = new some_fn2();  		x2.exe('a');  		x2.exe('b');  		x2.exe('c');  		a_fn2.push(x2);  	}  };
<button onclick="run_local_obj(this)">local obj</button>  <button onclick="run_proto_obj(this)">proto obj</button>  <button onclick="run_local_fn(this)">local obj fn</button>  <button onclick="run_proto_fn(this)">proto obj</button>

i have heard phrase:

closure variable defined each time function runs

but still, i'ts foggy.

i tried run measurements , first noticed is hard understand going on using code question.

if run these tests one-by-one (clicking @ buttons , looking @ timeline) each next run results differ much. few runs looked third (run_local_fn) longer others.

then tried run them in backward order (click buttons 4 1) , got different result - run_local_obj longest.

so modified test code bit, able stable results.

full code is here, can clone repo , test locally.

here how run each test in chrome (i launched using python -m simplehttpserver 8082 inside js-perf-test folder):

  • open tab http://localhost:8082/perf.html, open dev tools
  • start timeline recording
  • click button
  • wait results in console (min/max/mean)
  • stop timeline recording

results stable , repeatable (both timings , timeline view), here 1 of tests:

so see here is:

1) run_proto_obj fastest , run_local_obj close it.

i think expected run_proto_obj efficient since uses statically defined object strings. , js engine able optimize run_local_obj, x object re-used , not created each time.

2) run_local_fn slowest.

here have local x object , dynamic strings calculation, more floating parts in other tests.

3) run_proto_fn faster run_local_fn, slower first 2 functions.

i think expected, object a, b, c defined once (so faster run_local_fn).

and comparing first 2 functions, calculates resulting strings dynamically, slower.

so question:

as expected run_proto_fn run few times faster , minimal garbage collections, , low memory heap. run_proto_obj happened make exact opposite, if costly having non-function values @ object prototype property properties.

it looks me didn't setup experiment properly. according results above, run_proto_obj fastest.

update: tried same test in firefox, results similar:

  • `run_local_obj' - 344.85ms
  • `run_proto_obj' - 151.47ms
  • `run_local_fn' - 788.08ms
  • `run_proto_fn' - 265.21ms

the run_proto_obj fastest , run_local_fn slowest.


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