String concat vs array join

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

Shazzer Elite

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
1stFirefox152.0	6.00 ms	9.00 ms	Snippet A1.50× faster
2ndChrome150.0.0.0	14.80 ms	31.20 ms	Snippet A2.11× faster

Median of 5 trials × 20,000 iterations per snippet.