Cvars

A cvar is a server setting with a name: mp_freezetime, sv_gravity, or one of your plugin's own. A Cvar object reads and writes one:

const 
freezeTime
 = new 
Cvar
("mp_freezetime");
const 
speed
 = new 
Cvar
("myplugin_speed", "250");   // created with "250" if the server has no such cvar

speed
.
addEventListener
("change", (
event
) => {
    
console
.
log
(`${
event
.
cvar
.
name
}: ${
event
.
oldValue
} -> ${
event
.
value
}`);
});

function startWarmup() {
    
freezeTime
.
number
 = 0;
    
console
.
log
(`speed ${
speed
.
number
}, text "${
speed
.
value
}", on: ${
speed
.
boolean
}`);
}

Like an input's value, a cvar is text underneath, and it can be read and written three ways:

The second argument of new Cvar is the default. When the server has no cvar by that name, it is created with that value - the way a plugin adds its own settings. Without a default, a missing cvar stays missing: exists is false, reading gives "", 0 and false, and writing does nothing.

Make a Cvar once, at the top of the file, and use it from there. A Cvar made at the top of the file finds its cvar once the server has loaded every plugin, so the game's own cvars and those of other plugins are there by the time your code reads them.

Hearing a change

addEventListener("change", listener) calls the listener on every change - from the console, from amx_cvar, from another plugin or from this one - with event.cvar, event.oldValue and event.value (both as text). removeEventListener("change", listener) with the same function stops it.

A plugin that reads its settings once can do it in the "configsExecuted" event, after the server has run its config files (Plugin):

const 
reward
 = new 
Cvar
("myplugin_reward", "300");
let 
rewardMoney
 = 0;

server
.
addEventListener
("configsExecuted", () => {
    
rewardMoney
 = 
reward
.
number
;
});

For settings richer than a few numbers - lists, nested sections, per-map values - a config file is often the better place (Configs).