foo.js

var s1 = "http://"
var s2 = "ftp://"
var s3 = "htts://"
var total = 100000000;
var n;
var start;

n = 0;
start = Date.now();
for (var i = 0; i < total; i++) {
  switch (i % 3) {
  case 0:
    if (s1[0] == 'h' && s1.substring(0, 4) === 'http') n++;
    break
  case 1:
    if (s2[0] == 'h' && s2.substring(0, 4) === 'http') n++;
    break
  case 2:
    if (s3[0] == 'h' && s3.substring(0, 4) === 'http') n++;
    break
  }
}
console.assert(n == Number(total / 3 + 0.5).toFixed() * 1);
console.log(Date.now() - start);

n = 0;
start = Date.now();
for (var i = 0; i < total; i++) {
  switch (i % 3) {
  case 0:
    if (s1.substring(0, 4) === 'http') n++;
    break
  case 1:
    if (s2.substring(0, 4) === 'http') n++;
    break
  case 2:
    if (s3.substring(0, 4) === 'http') n++;
    break
  }
}
console.assert(n == Number(total / 3 + 0.5).toFixed() * 1);
console.log(Date.now() - start);

n = 0;
start = Date.now();
for (var i = 0; i < total; i++) {
  switch (i % 3) {
  case 0:
    if (s1.startsWith('http')) n++;
    break
  case 1:
    if (s2.startsWith('http')) n++;
    break
  case 2:
    if (s3.startsWith('http')) n++;
    break
  }
}
console.assert(n == Number(total / 3 + 0.5).toFixed() * 1);
console.log(Date.now() - start);