redos.go

package main

import (
	"fmt"
	"regexp"
	"strings"
	"time"
)

func main() {
	for i := 0; i < 1000; i++ {
		check(i)
	}
}

func check(i int) {
	// don't include compilation time as this is a static cost
	re := regexp.MustCompile(fmt.Sprintf("^(?:a?){%[1]d}a{%[1]d}$", i))
	payload := strings.Repeat("a", i)

	start := time.Now()
	re.MatchString(payload)
	fmt.Printf("%d\t%.9f\n", i, time.Since(start).Seconds())
}

redos.js

"use strict";

for (var i = 0; i < 1000; i++) {
	check(i);
}

function check(i) {
	// don't include compilation time as this is a static cost
	var re = new RegExp("^(?:a?){" + i + "}a{" + i + "}$");
	var payload = new Array(i + 1).join("a");

	var start = process.hrtime();
	re.test(payload);
	var diff = process.hrtime(start);
	console.log(i + "\t" + (diff[0] + diff[1] * 1e-9).toFixed(9));
}