Is it possible to have an event in JS that fires when the value of a certain variable changes? JQuery is accepted.
No.
But, if it's really that important, you have 2 options (first is tested, second isn't):
First, use setters and getters, like so:
var myobj = {a : 1};
function create_gets_sets(obj) { // make this a framework/global function
var proxy = {}
for ( var i in obj ) {
if (obj.hasOwnProperty(i)) {
var k = i;
proxy["set_"+i] = function (val) { this[k] = val; };
proxy["get_"+i] = function () { return this[k]; };
}
}
for (var i in proxy) {
if (proxy.hasOwnProperty(i)) {
obj[i] = proxy[i];
}
}
}
create_gets_sets(myobj);
then you can do something like:
function listen_to(obj, prop, handler) {
var current_setter = obj["set_" + prop];
var old_val = obj["get_" + prop]();
obj["set_" + prop] = function(val) { current_setter.apply(obj, [old_val, val]); handler(val));
}
then set the listener like:
listen_to(myobj, "a", function(oldval, newval) {
alert("old : " + oldval + " new : " + newval);
}
Second, you could put a watch on the value:
Given myobj above, with 'a' on it:
function watch(obj, prop, handler) { // make this a framework/global function
var currval = obj[prop];
function callback() {
if (obj[prop] != currval) {
var temp = currval;
currval = obj[prop];
handler(temp, currval);
}
}
return callback;
}
var myhandler = function (oldval, newval) {
//do something
};
var intervalH = setInterval(watch(myobj, "a", myhandler), 100);
myobj.set_a(2);