! is a way of saying "not". Not i is therefore true if i is false, and vice versa.

You are a genius, can I have children for you? xd

var scriptName = "DommeTimer";
var scriptVersion = 0.1;
var scriptAuthor = "Domme"

var Title = new Title()
var client;

function Title() {

    this.getName = function() {
        return "DommeTimer"
    }

    this.getDescription = function() {
        return "on-off Timer thing"
    }

    this.getCategory = function() {
        return "Fun"
    }
    var i = false,
        secs = 1.0;

    this.onUpdate = function(event) {

        if (mc.thePlayer.timerSpeed % (secs * 20) == 0) {
            if (i) {
                mc.timer.timerSpeed = 1.5;
            } else {
                mc.timer.timerSpeed = 1;
            }

            i = !i;
        }
    }

    this.onDisable = function() {
        mc.timer.timerSpeed = 1;
    }

}

function onEnable() {
    client = moduleManager.registerModule(Title)
}

function onDisable() {
    moduleManager.unregisterModule(client)
}

Let's go through the main code one by one:

var i = false, secs = 1.0;
This declares 2 variables, i and secs.
secs is the amount of seconds you want it to timer for, i determines whether to make timer faster or slower.

if(i)
This is a shorthand for i == true.

mc.timer.timerSpeed = 1.5;
This sets the timer value to 1.5, making the game 50% faster.

else
This is like saying "if the previous statement is false, do this".

i = !i;
This sets i to it's inverse. In programming, ! is a way of saying "not". Not i is therefore true if i is false, and vice versa.

why are you laughing?
also, as fact, in English countries people do not use 'haha' or 'ahah' when typing. They use 'LMAO' as far as i know

Im from rus. Pls send me Core.Lib

your grammar is the worst in this fucking world

Ahah, I didn't fully learn javascirpt

moduleManager.getModule("Timer").getValue("Speed").set(1.5);

when you can

timer.timerSpeed = 1.5;