Javascript variable that always returns value of function

Question

I'm pretty sure I know the answer to this (and that it is no), but is it possible to create a variable that always returns the value of a function without "calling" the variable?

I'm sick of an inactivity warning on a website I use. I look at it a few times a day, but I keep it open in case there's an update I need to look at. It automatically signs me out after 15 minutes using some javascript--the token isn't invalidated by a cookie expiring, nor is my session removed server-side--and the variable it checks is called last_user_action.

I'd like to make last_user_action always point to new Date().getTime();.

last_user_action = function() { new Date().getTime(); }

would work if I could easily change all the references to last_user_action to instead belast_user_action(), but I can't.

last_user_action = (function() { return new Date().getTime(); })();

only sets the value once.

So like I said, I doubt there's a way to do this, but if it is possible, how would I do it?

EDIT It occurs to me now, it'd be easier to just run

window.setInterval(function() { last_user_action = new Date().getTime(); }, 1000 * 60 * 10);

in Chrome's javascript console.

setInterval(function(){last_user_action = new Date().getTime();}, 1000) — GSerg
– GSerg, Commented Oct 9, 2014 at 19:14

juvian · Accepted Answer · 2014-10-09 19:15:15Z

4

Well, if you are sure it works that way, you could use setInterval every minute to set the value:

setInterval(function(){
    last_user_action = new Date().getTime();
},60000)

answered Oct 9, 2014 at 19:15

juvian

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Chris Hayes · Accepted Answer · 2014-10-09 19:14:19Z

2

Not that directly, but it would be trivial to just update the variable periodically.

function updateLastUserAction() {
    last_user_action = new Date().getTime(); // or Date.now();
    setTimeout(updateLastUserAction, 10000); // run again in 10 seconds
}

updateLastUserAction();

You can change the update period to suit you - since the update function is extremely lightweight, you can run it pretty often and it won't matter.

answered Oct 9, 2014 at 19:14

Chris Hayes

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Comments

Alex Wayne · Accepted Answer · 2014-10-09 19:16:09Z

2

Assuming last_user_action is a global variable, that means it's actually a property of window and you can define a getter for that property.

Object.defineProperty(window, 'last_user_action', {
  get: function() {
    return new Date().getTime();
  }
});
last_user_action; // 1412882205169
last_user_action; // 1412882206490

This would normally be a bad idea, but given you are hacking here, it doesn't seem so bad.

answered Oct 9, 2014 at 19:16

Alex Wayne

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Comments

Oriol · Accepted Answer · 2014-10-09 19:14:27Z

1

AFAIK you can't do that with a variable.

But you can do it with a property, using a getter:

var obj = {};
Object.defineProperty(obj, 'last_user_action', {
    get: function() { return new Date().getTime(); }
});
obj.last_user_action; // Current date time

answered Oct 9, 2014 at 19:14

Oriol

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