How to set a persistent global timeout using a Tampermonkey/Greasemonkey script?

Question

I am trying to redirect the tab to, say, http://google.com every few minutes, no matter what happened to the tab (it is still open of course).

I am using:

setTimeout(function() {
    window.location.href = "http://google.com";
}, 500000);

However the counter refreshes as soon I load a new page in the tab.
Is there a way to set a global time countdown for the tab so that no matter what I load, I still get redirected every few minutes?

Answer 1

One way to persist the timer between page loads is to use GM_setValue()^Doc.

Here's a complete Tampermonkey/Greasemonkey script that illustrates the process:

// ==UserScript==
// @name     _Persistent redirect timer
// @include  http://YOUR_SERVER.COM/YOUR_PATH/*
// @grant    GM_getValue
// @grant    GM_setValue
// ==/UserScript==
var timerLength = 500000;   //- 500,000 milliseconds

var timerStart  = GM_getValue ("timerStartKey");
if (timerStart)
    timerStart  = JSON.parse (timerStart);
else
    resetTimerStart ();

/*-- RECOMMENDED: If too much time has passed since the last page load,
    restart the timer.  Otherwise it will almost instantly jump to the
    redirect page.
*/
checkElapsedAndPossiblyRedirect (true);
console.log ("timerStart: ", timerStart);

//-- Polling every 10 seconds is plenty
setInterval (checkElapsedAndPossiblyRedirect, 10 * 1000);

function resetTimerStart () {
    timerStart  = new Date().getTime ();
    GM_setValue ("timerStartKey", JSON.stringify (timerStart) );
}

function checkElapsedAndPossiblyRedirect (bCheckOnly) {
    if ( (new Date().getTime() ) - timerStart  >=  timerLength) {
        resetTimerStart ();
        if ( ! bCheckOnly) {
            console.log ("Redirecting.");
            window.location.href = "http://google.com";
        }
    }
}

Depending on your intentions, you may wish to comment out the checkElapsedAndPossiblyRedirect (true); line. But, things could get confusing if you do.