benchmark of String.startsWith equivalents in Node.js

benchmark-startswith.js

var Benchmark = require('benchmark');
Benchmark.prototype.setup = function() {
  a = ["test"];
  for (var i = 0; i < 10000; i++) {
    a.push("some other stuff");
  }
  s = a.join();
  re1 = new RegExp("^test");
  re2 = new RegExp("^not there");
};
var suite = new Benchmark.Suite();

// add tests
suite.add('indexOf', function() {
  var r1 = (s.indexOf("test") === 0);
  var r2 = (s.indexOf("not there") === 0);
})
  .add('lastIndexOf', function() {
  var r1 = (s.lastIndexOf("test", 0) === 0);
  var r2 = (s.lastIndexOf("not there", 0) === 0);
})
  .add('substring', function() {
  var r1 = (s.substring(0, "test".length) == "test");
  var r2 = (s.substring(0, "not there".length) == "not there");
})
  .add('slice', function() {
  var r1 = (s.slice(0, "test".length) == "test");
  var r2 = (s.slice(0, "not there".length) == "not there");
})
  .add('regex', function() {
  var r1 = (/^test/).test(s);
  var r2 = (/^not there/).test(s);
})
  .add('compiled regex', function() {
  var r1 = re1.test(s);
  var r2 = re2.test(s);
})
// add listeners
.on('cycle', function(event) {
  console.log(String(event.target));
})
  .on('complete', function() {
  console.log('Fastest is ' + this.filter('fastest').pluck('name'));
})
// run async
.run({
  'async': false
});

indexOf x 4,724 ops/sec ±8.30% (51 runs sampled)
lastIndexOf x 1,970,353 ops/sec ±0.22% (67 runs sampled)
substring x 2,348,729 ops/sec ±5.86% (62 runs sampled)
slice x 2,009,238 ops/sec ±5.15% (62 runs sampled)
regex x 2,140,300 ops/sec ±1.21% (64 runs sampled)
compiled regex x 2,241,266 ops/sec ±0.96% (62 runs sampled)
Fastest is compiled regex,slice

I suppose lastIndexOf must be the fastest, which is true for Firefox (see: http://jsperf.com/string-startswith/3 )

indexOf x 12,782 ops/sec ±81.75% (13 runs sampled)
lastIndexOf x 7,163,640 ops/sec ±7.38% (60 runs sampled)
substring x 10,142,306 ops/sec ±10.17% (55 runs sampled)
slice x 7,855,020 ops/sec ±10.90% (56 runs sampled)
regex x 9,497,811 ops/sec ±6.89% (62 runs sampled)
compiled regex x 10,821,279 ops/sec ±6.57% (69 runs sampled)
Fastest is compiled regex,substring

node v0.10.35
何度か試行しましたが、compiled regex, substringとなるケースが多いようでした。

Update April 2020 since this is still the first Google result for node js startswith performance.

indexOf            113,625 ops/sec ±3.51% (78 runs sampled)
startsWith      22,522,847 ops/sec ±0.20% (94 runs sampled)
lastIndexOf     19,520,195 ops/sec ±0.41% (92 runs sampled)
substring    1,368,227,502 ops/sec ±0.07% (95 runs sampled)
slice        1,360,307,286 ops/sec ±0.07% (93 runs sampled)
regex           26,319,865 ops/sec ±1.17% (91 runs sampled)
comp regex      19,868,632 ops/sec ±3.01% (87 runs sampled)
Fastest is substring

Added str.startsWith() and tested on Node v12.16.2.
The edited code is available HERE

How to run this via command line?

$ time node starts-with.js

indexOf:
startsWith:
lastIndexOf:
substring:
slice:
regex:
compiled regex:
>Fastest is

node starts-with.js  0.10s user 0.01s system 99% cpu 0.117 total

You can use repeat() to multiply a string

> 'abc'.repeat(100)

'abcabcabcabcabcabcabcabcabcabcabcabcabcabcabcabcabcabcabcabcabcabcabcabcabcabcabcabcabcabcabcabcabcabcabcabcabc
abcabcabcabcabcabcabcabcabcabcabcabcabcabcabcabcabcabcabcabcabcabcabcabcabcabcabcabcabcabcabcabcabcabcabcabcabc
abcabcabcabcabcabcabcabcabcabcabcabcabcabcabcabcabcabcabcabcabcabcabcabcabcabc'

I had to use simplification method

var str_repeat = 100
var checks = 1000000

var start = 'start text'
var not_there = 'not there'

var str = start + 'some string'.repeat(str_repeat)

console.time()

for (let i = 0; i < checks; i++)    
    str.startsWith(start)

console.timeEnd()

$ time node starts-with.js

default: 63.477ms
node starts-with.js  0.09s user 0.01s system 98% cpu 0.100 total