String concat vs array join

Compares building a string with += concatenation against Array.prototype.join for assembling many pieces.

Shazzer Master

Created Jul 4, 2026

Updated Jul 4, 2026

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CategoryJavaScript Syntax

VisibilityPublic

TypePERF

CharsetUTF-8

Code used before fuzz:

var iterations = 20000;0x0D
var parts=Array.from({length:100},function(_,i){return "x"+i});

Snippet A:

var r="";for(var i=0;i<parts.length;i++){r+=parts[i]}

Snippet B:

parts.join("")

Sample payloads

var r="";for(var i=0;i<parts.length;i++){r+=parts[i]}

parts.join("")

Snippet A

var r="";for(var i=0;i<parts.length;i++){r+=parts[i]}

Snippet B

parts.join("")

Browser	Snippet A	Snippet B	Winner
1stFirefox153.0	4.00 ms	7.00 ms	Snippet A1.75× faster
2ndSafari26.5.2	9.00 ms	12.00 ms	Snippet A1.33× faster
3rdChrome151.0.7922.137	9.30 ms	25.00 ms	Snippet A2.69× faster
4thMicrosoft Edge151.0.4129.59