Benchmarking String Concatenation

gistfile1.js

// Benchmarking String Concatenation Comparing
//   1. Array.join
//   2. String concatenation with '+'

// Test Functions
function test_join(content) { return ['output.push(', content, ');'].join(''); };
function test_str_concat(content) { return 'output.push(' + content + ');'; };

// Test Strings
var SHORT_STRING = 'test';
var LONG_STRING = SHORT_STRING;
for (var i=0; i<1e3; ++i) LONG_STRING += SHORT_STRING;

// Verify they do the same thing
var s1 = test_join(SHORT_STRING);
var s2 = test_str_concat(SHORT_STRING);
console.log( s1 );
console.log( s2 );
if ( s1 != s2 ) console.log('Different Outputs.');

// -----
// Test 1. Array.join on a short string
// -----
(function(){
    var s = (new Date()).getTime();
    for (var i=0; i<1e5; i++) { test_join(SHORT_STRING); }
    var e = (new Date()).getTime();
    console.log( (e-s) + 'ms' );
})();

// -----
// Test 2. Array.join on a long string
// -----
(function(){
    var s = (new Date()).getTime();
    for (var i=0; i<1e5; i++) { test_join(LONG_STRING); }
    var e = (new Date()).getTime();
    console.log( (e-s) + 'ms' );
})();

// -----
// Test 3. String concat on a short string
// -----
(function(){
    var s = (new Date()).getTime();
    for (var i=0; i<1e5; i++) { test_str_concat(SHORT_STRING); }
    var e = (new Date()).getTime();
    console.log( (e-s) + 'ms' );
})();

// -----
// Test 4. String concat on a long string
// -----
(function(){
    var s = (new Date()).getTime();
    for (var i=0; i<1e5; i++) { test_str_concat(LONG_STRING); }
    var e = (new Date()).getTime();
    console.log( (e-s) + 'ms' );
})();

// -----
// Results on my Leopard Mac with Firefox 3
// -----
//    Tests                           |  Average
// ----------------------------------------------
// 1. 651ms, 595ms, 590ms, 592ms     =>   607.00
// 2. 1204ms, 1086ms, 1083ms, 1068ms =>  1110.25
// 3. 146ms, 136ms, 134ms, 134ms     =>   137.50
// 4. 1008ms, 969ms, 962ms, 981ms    =>   980.00

// -----
// Notes
// -----
//
//  1. I don't know the typical usage for the function, but
//     it seems like for short stings its faster to just '+'
//  2. My tests ran 1e5 times, thats 1 million times, and the
//     results are low enough that you probably won't see
//     any performance difference at a low number of
//     invokations.  [See #1]
//  
//  - Joseph Pecoraro
//