How did you test the functions for the speed comparison?

I compared your method, the + and += operators, and the native String.concat() function, but in all browsers the .contact function beats the other methods of string concatenation.

Results for 10000 repetitions:
StringBuilder += String.concat()
IE6 94ms 531ms 16ms
IE7 110ms 672ms 15ms
IE8 63ms 15ms 16ms
FF3 43ms 5ms 4ms

In Firefox 3.0 and IE8 the + and += operators perform even better than your function in my test, your function only performs better in IE6 and IE7.

But I only used a simple loop to concatenate strings, so I was curious about how you got your test results.

start=new Date()
s=”
for (i=0;i<1000000;i++) s+=’Hello World’
sl=s.length
end=new Date()
document.writeln(’string ‘,end.getTime()-start.getTime())

start=new Date()
sb=new StringBuilder()
for (i=0;i<1000000;i++) sb.append(’Hello World’)
sbl=sb.toString().length
end=new Date()
document.writeln(’StringBuffer ‘,end.getTime()-start.getTime())

And the results :

– FireFox 3.0.10 :
string 991
StringBuffer 10177

– SeaMonkey 1.1.16 :
string 2611
StringBuffer 16216

– Opera 9.64 :
string 816
StringBuffer 4510

– Midori 0.1.6 :
string 1773
StringBuffer 2332