In javascript, how to trigger event when a variable's value is changed? [duplicate]

Question

I have two variables:

var trafficLightIsGreen = false; 
var someoneIsRunningTheLight = false;

I would like to trigger an event when the two variables agree with my conditions:

if(trafficLightIsGreen && !someoneIsRunningTheLight){
    go(); 
}

Assuming that those two booleans can change in any moment, how can I trigger my go() method when they change according to the my conditions?

Answer 1

There is no event which is raised when a given value is changed in Javascript. What you can do is provide a set of functions that wrap the specific values and generate events when they are called to modify the values.

function Create(callback) {
  var isGreen = false;
  var isRunning = false;
  return { 
    getIsGreen   : function()  { return isGreen; },
    setIsGreen   : function(p) { isGreen = p; callback(isGreen, isRunning); },
    getIsRunning : function()  { return isRunning; },
    setIsRunning : function(p) { isRunning = p; callback(isGreen, isRunning); }
  };
}

Now you could call this function and link the callback to execute go():

var traffic = Create(function(isGreen, isRunning) {
  if (isGreen && !isRunning) {
    go();
  }
});

traffic.setIsGreen(true);

Answer 2

//ex:
/*
var x1 = {currentStatus:undefined};
your need is x1.currentStatus value is change trigger event ?
below the code is use try it.
*/
function statusChange(){
    console.log("x1.currentStatus_value_is_changed"+x1.eventCurrentStatus);
};

var x1 = {
    eventCurrentStatus:undefined,
    get currentStatus(){
        return this.eventCurrentStatus;
    },
    set currentStatus(val){
        this.eventCurrentStatus=val;
    }
};
console.log("eventCurrentStatus = "+ x1.eventCurrentStatus);
x1.currentStatus="create"
console.log("eventCurrentStatus = "+ x1.eventCurrentStatus);
x1.currentStatus="edit"
console.log("eventCurrentStatus = "+ x1.eventCurrentStatus);
console.log("currentStatus = "+ x1.currentStatus);

Answer 3

The most reliable way is to use setters like that:

var trafficLightIsGreen = false; 
var someoneIsRunningTheLight = false;

var setTrafficLightIsGreen = function(val){
    trafficLightIsGreen = val;
    if (trafficLightIsGreen and !someoneIsRunningTheLight){
        go(); 
    };
};
var setSomeoneIsRunningTheLight = function(val){
    trafficLightIsGreen = val;
    if (trafficLightIsGreen and !someoneIsRunningTheLight){
        go(); 
    };
};

and then instead of assigning a value to a variable, you just invoke the setter:

setTrafficLightIsGreen(true);