bar.js

'use strict';

const ITERATION = 100000000;
const DATA = [
  'http://',
  'ftp://',
  'htts://',
  '',
];
const FUNCS = [
  ishttp0,
  ishttp1,
  ishttp4,
];

FUNCS.forEach(function(f) {
  bench(f, ITERATION);
});

function bench(f, n) {
  var st = Date.now();
  var cnt = 0;
  for (var i = 0; i < n; ++i) {
    if (f(DATA[i % DATA.length])) {
      ++cnt;
    }
  }
  console.log(Date.now() - st, cnt);
}

function ishttp0(s) {
  return s[0] === 'h' && s[1] === 't' && s[2] === 't' && s[3] === 'p';
}

function ishttp1(s) {
  return s[0] === 'h' && s.substring(0, 4) === 'http';
}

function ishttp2(s) {
  return s.substring(0, 4) === 'http';
}

function ishttp3(s) {
  return s.startsWith('http');
}

function ishttp4(s) {
  return startsWith(s, 'http');
}

function startsWith(s, t) {
  if (s.length < t.length) {
    return false;
  }
  for (var i = 0; i < t.length; ++i) {
    if (s[i] !== t[i]) {
      return false;
    }
  }
  return true;
}