Have Greasemonkey click a button at first load and then in intervals?

Question

I'm trying to make Greasemonkey script that clicks on a button at intervals and also clicks on it at the first load without wait.

I made this code which clicks every 120 seconds but the first time the page loads I have to wait 120 seconds for the code to click the GO button or I have to manually do it. :

window.setTimeout(function(){document.getElementById("masterPage_cphPageBody_btnGo").click()},120000)

and here is the source code related to it from the website

<input id="masterPage_cphPageBody_btnGo" name="masterPage$cphPageBody$btnGo" value="Go" onclick="SetSearchDate();showWaitpage();" class="btn2" type="submit">

How can I add a line to click on the GO the first time the page loads and 120 seconds there after?

the webpage before and after pressing the GO button has the same exact URL so adding the click on GO button without wait time will send hte page into a loop of URL loaded GO clicked
URL Loaded GO clicked URL Loaded GO clicked ...

checked the differences of the page before and after the first time GO button is clicked...

so I need the script to click Go button immidiately only if the following page does NOT show on the page

<span id="masterPage_cphPageBody_lblSelectAvailableTime" class="bodyBold">Select an available time</span>

but if "Select an available time" text show on page the script should wait 120 secon

I'm running: Greasemonkey, Windows 8 64, Firefox

Answer 1

Use a named function instead on an anonymous one (Often a good idea anyway).

Then use document.querySelector to check if that element is present. _{(That function has much more flexibility than getElementById.)}

So your code becomes:

if (null === document.querySelector ("#masterPage_cphPageBody_lblSelectAvailableTime") ) {
    clickGoButton ();  //-- Initial, immediate click.
}

window.setTimeout (clickGoButton, 120000);

function clickGoButton () {
    document.getElementById ("masterPage_cphPageBody_btnGo").click ();
}