Should I statically allocate Javascript strings for memory performance?

Question

So, I am writing this node.js application and I am trying to make it very fast and low in memory. I have a lot of string concatenation such as:

function f(pt) { 
    return pt.x + ' + ' + pt.y; 
}

If I do it like 100 million times right in the inner loop of my application, does the Javascript engine allocate and should free this line ' + '100 million times? It would be more memory intensive to rewrite this code as something like

var plus = ' + ';
function f(pt) { 
    return pt.x + plus + pt.y; 
}

Or does the compiler just do it in the background, or does it even not matter? (My code does use much longer lines than "+", I just used this as an example.)

Answer 1

.

, , . , plus , , , .

, , .

:

console.time('plus outside');
var plus=' x ', fn=function(pt){return pt.x + plus + pt.y};
for(var i=0; i<1e5; i++){ fn({x:5,y:6}); }
console.timeEnd('plus outside');

:

console.time('plus inside');
var fn=function(pt){return pt.x + ' + ' + pt.y};
for(var i=0; i<1e5; i++){ fn({x:5,y:6}); }
console.timeEnd('plus inside');

Google Chrome v41.0.2272.89 m, plus outside 200 , 175 ms!
25% !

:

!

window.onload=function(){

	(function(elem){
		
		var plus=' + ',fn=function(pt){return pt.x + plus + pt.y}, start=new Date();
      
		for(var i=0; i<1.5e7; i++){ fn({x:5,y:6}); };
		var end=new Date();
		
		elem.innerHTML=(end-start)+'ms (i:'+i+')';
		
	})(document.getElementById('plus_outside'));
  
  
  
	
	(function(elem){
		
		var fn=function(pt){return pt.x + ' + ' + pt.y}, start=new Date();
      
		for(var i=0; i<1.5e7; i++){ fn({x:5,y:6}); };
		var end=new Date();
		
		elem.innerHTML=(end-start)+'ms (i:'+i+')';
		
	})(document.getElementById('plus_inside'));
  
  
	
	(function(elem){
		
		var fn=function(pt){return [pt.x,'+',pt.y].join(' ')}, start=new Date();
      

		for(var i=0; i<2e5; i++){ fn({x:5,y:6}); };
		var end=new Date();
		
		elem.innerHTML=(end-start)+'ms (i:'+i+')';
		
	})(document.getElementById('array'));
  
  
  	(function(elem){
		
		var fn=function(pt){return [pt.x,' + ',pt.y].join('')}, start=new Date();
      

		for(var i=0; i<2e5; i++){ fn({x:5,y:6}); };
		var end=new Date();
		
		elem.innerHTML=(end-start)+'ms (i:'+i+')';
		
	})(document.getElementById('array_nojoin'));
  
  
  
   (function(elem){
		
		var fn=function(pt){return ([pt.x,'+',pt.y]+'').replace(',',' ')}, start=new Date();
      

		for(var i=0; i<2e5; i++){ fn({x:5,y:6}); };
		var end=new Date();
		
		elem.innerHTML=(end-start)+'ms (i:'+i+')';
		
	})(document.getElementById('array_replace'));
  

};

<font face="sans-serif">
<p>
  Plus inside: <span id="plus_inside"></span><br>
  &nbsp;&nbsp;fn: <code>function(pt){return pt.x + ' + ' + pt.y}</code>
</p>

<p>
  Plus outside: <span id="plus_outside"></span><br>
  &nbsp;&nbsp;fn: <code>function(pt){return pt.x + plus + pt.y}</code>
</p>

<p>
  Array: <span id="array"></span><br>
  &nbsp;&nbsp;fn: <code>function(pt){return [pt.x,'+',pt.y].join(' ')}</code>
</p>

<p>
  Array (no join): <span id="array_nojoin"></span><br>
  &nbsp;&nbsp;fn: <code>function(pt){return [pt.x,' + ',pt.y].join('')}</code>
</p>


<p>
  Array (replace comas): <span id="array_replace"></span><br>
  &nbsp;&nbsp;fn: <code>function(pt){return ([pt.x,'+',pt.y]+'').replace(',',' ')}</code>
</p>
</font>

Hide result

Answer 2

. .

["a","b","c"].join('');

, - , .

Answer 3

, , , V8 (Chrome) , ' + '. , , .

, ( ):

var f = function(a, b) { return a + ' + ' + b; };

:

var c = f('1', '2');

, :

"1 + 2"

, , , . .

: -, , . , .