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I need help creating a loop in dev console in firefox

I am trying to use the dev console to give mario a mushroom every 5 seconds (in the browser game super mario html5)
I can give mario mushrooms manually by typing marioShroons(mario) but I would like to have it on loop so I don't have to pause the game every time I want a mushroom. I have tried a while loop and set timeout but I can't figure it out. The only coding languages I familiar with are c++ and html.
**
while(data.time.amount > 0) {
killOtherCharacters()
}
setTimeout(function() {
killOtherCharacters()
}, 1000);
I expected these lines of code to not give me a mushroom, but to automatically kill enemies. But on the first try (the while loop) it froze the tab and I had to reload the page.
With the set timeout, it didn't make any obvious results, it killed all near characters once and then stopped.

You tried using setTimeout, and it only worked once. This is to be expected, because:
Window.setTimeout() sets a timer which executes a function or specified piece of code once the timer expires
From MDN
What you need to do is use setInterval:
The setInterval() method...repeatedly calls a function or executes a code snippet, with a fixed time delay between each call.
From MDN
So in your console, you should write this:
setInterval(killOtherCharacters, 1000);
(I removed the anonymous function because it wasn't needed - you only need an anonymous function if you're passing parameters or doing multiple things. You do need to remove the () for this though).
And if you want to stop the function from executing, assign a variable to the interval:
var killCharacters = setInterval(killOtherCharacters, 1000);
Then call clearInterval upon this variable to clear the interval (stop the loop):
clearInterval(killCharacters);

The reason your while loop froze the page is because Javascript can only do one thing at a time and you told it to always run your while function, blocking all other Javascript from running on your site.
setTimeout is only run once after a set time (see documentation), if you want to run something every x miliseconds it's better to use setInterval instead.
var intervalID = window.setInterval(killOtherCharacters(), 500); //run this every 500 ms

Use setInterval if you want killOtherCharacters() to be called repeatedly.
const interval = setInterval(function() {killOtherCharacters() },1000);
Then when you want the function to stop being called:
clearInterval(interval);

jwplayer onTime() calling setInterval() several times per second

My main goal is at 7:45 in the video to display a countdown timer from 20:00.
Here is my event called by the jwplayer I'm using:
onTime: function(event){showTimer(event.position);}
Here is my funciton showTimer:
function showTimer(video_position){
// Schedule the update to happen once every second
if(Math.round(video_position) == 465){
setInterval(updateTimer, 1000);
}
};
The Problem:
Because it onTime() isn't guaranteed to hit right at 465.0 I have to d a Math.round on the video position. If I do this, 4-10 onTime event handlers knock off within 465.0 - 466.0 so my setInterval() gets called several times and the timer counts down insanely fast.
Is there a way to make it hit the setInterval() once or maybe a global variable I can set the first time to let setInterval() know its already been knocked off?

I'd just use a boolean flag to check whether the event has fired yet.
var fired = false;
if(Math.round(video_position) == 465 && !fired){
fired = true;
setInterval(updateTimer, 1000);
}
That way it can only fire the event once.

Why the fiddle is not working and there is a time lag behind in following case?

My fiddle link is as follows:http://jsfiddle.net/FvYyS/2/
The function call is as follows:
load_timer('0', '6', '9', 0, '0', '', '0');
Actually my issue is the fiddle is not working. The expected behaviour of this code is the timer should decrease second by second and ultimately reaches to zero(i.e. for example the timer should start at 00:06:09 and end at 00:00:00). But it's not working here in the fiddle. The code is working properly in my application but don't know why this code is not working in fiddle. Also one more issue I noticed in my application is the timer is lagging sometime behind. Can anyone please help me in this regard? If you need any further information I'll provide you the same. Thanks in advance.

Your code has the following structure :
var counter = delay;
function loop() {
counter--;
displayTime(delay, counter);
if (counter > 0) {
setTimeout( loop, 1000 );
}
}
2 things :
displayTime() execution takes time : for example, if it takes 0.2 seconds to complete, the loop will be executed every 1.2 seconds (instead of every second)
setTimeout( ..., 1000 ) means "Please dear javascript runtime, can you run my code in 1 second ? If you have other stuff to do, it is ok for me to wait more."
You have the guarantee that there will be at least 1 second between the setTimeout call and your loop excution, but the delay can be longer.
If you want to avoid the time drift, check for the real time on each iteration :
var start = Date.now();
function loop() {
var now = Date.now();
var elapsedTime = now - start; //elapsed time in milliseconds
displayTime(delay, elapsedTime);
if (elapsedTime < delay) {
setTimeout(loop, 1000);
}
}

you have not included the jquery library in your fiddle
See UPDATED FIDDLE

There are several problems with your approach:
Since you do the setTimeout after doing some work, the time it takes for your work to be done will delay the next iterations. You could fix this by moving the setTimeout call to be the first executed and then do the work.
Using setTimeout(f, timeout) guarantees that the f function will be executed at least timeout miliseconds after the setTimeout call. So if for example the browser is busy for 1 second when the call to f should be executed, the call to f is delayed by 1 second. Furthermore, the next call to setTimeout is delayed by that second, so everything coming after that will incur your delay.
A better fix would be to use setInterval which is designed with repeating a task every n miliseconds and alleviates the recurrent delay problem.
Finally, the best solution to the problem is to use Date to determine the start of your counter and show the exact time elapsed by substracting the original time from the current time.

how to create a timer which triggers an event after 30 seconds in javascript?

I am working on a module in which there is a requirement to show a timer which shows only seconds. The timer must start from 30 and keep on decrementing down to 0; and after that fire some action and again start from 30. How can I achieve this in javascript?

There you go :)
var timer = 30;
function decrementAfter1Second(){
setTimeout(function(){
timer--;
if(timer==0){
doWhateverYouWantAfter30Seconds();
timer = 30;
}
decrementAfter1Second();
}, 1000);
}
decrementAfter1Second();
Now next time you want to do something in javascript don't be a slacker and read something about the language first ;) because right now i'm assuming you either don't know how to program or you don't know how to use google.

You could use setTimeout and clearTimeout. Have the timeout fire every 1 second and then invoke clearTimeout when seconds == 0.
You can find examples of both functions here.

Help chosing between settimeout and setinterval

UPDATE 2:
OK, looks like it runs the first time after a minute. How do I get it to run onload, then every minute after that?
UPDATE 1:
I've tried: var interval = setInterval(get_reported_incidents, 60000); but nothing happens. in get_reported_incidents(); I just have an alert("hello");.
ORIGINAL QUESTION:
I want to run a function every minute:
get_reported_incidents();
But I am not sure which method is best for this task;
settimeout or setinterval

It's totally personal preference. setInterval has some odd edge cases around what happens when the previous interval's code hasn't finished running before the next interval is due to start (not a problem if your interval is every minute; intervals every second, which one sometimes wants, get a bit tricky).
I tend to prefer chained setTimeout calls (where each schedules the next) because they can't run away with you — your code always has to explicitly say "Okay, and call me back again next time." But properly-written code should work with either.
Chained setTimeout calls are also more well-suited to asynchronous operations, like for instance polling something via ajax, because you don't schedule the next timeout until the ajax operation completes. Using setInterval, because the ajax calls are asynchronous, you could end up overlapping them.

Using setinterval would be the more natural choise. If you use setTimeout, you have to start a new timeout from the event handler.
window.setInterval(get_reported_incidents, 60*1000);

setTimeout runs a command once after a period of time. setInterval runs a command every time interval.
So, to run get_reported_incidents every minute use setInterval.
var interval = setInterval(get_reported_incidents, 60000);

setinterval executes a function at a given interval. settimeout executes a function after a specified wait time, and then exits.
If you are attempting to do a cron-like execution every minute, you will want to use setinterval.
Please see http://javascript.about.com/library/blstvsi.htm for a comparison.

use setTimeout recursively. See here for more information on why setInterval is a poor choice.
function timeout (){
get_reported_incidents();
setTimeout(timeout, 1000 * 60);
}
timeout(); // start

Strictly speaking, setInterval() was designed for repeating events and setTimeout() for one-shot events.
However you will tend to find that with setTimeout() time will "creep" gradually. I've not tried this at 1 minute intervals, but with a 1 second timer I found it happened quite a lot. A clock showing the current time (to the nearest millisecond) would show a steady increase in the millisecond value of "now".
See http://jsfiddle.net/alnitak/LJCJU/ and tweak the interval to see what I mean!
So, for greatest accuracy, I do this:
var timerHandler = function() {
var interval = 60000;
// do some stuff
...
var now = new Date();
var delay = interval - (now % interval);
setTimeout(timerHandler, delay);
};
This is ideal if you want the timer events to be started in sync with the clock on your system, rather than at some unspecified time "roughly every minute".

obviously setinterval might be easier to maintain in your case
get_reported_incidents(); //first call
var interval = setInterval(get_reported_incidents, 60000);
vs
var interval;
function timeout (){
get_reported_incidents();
interval=setTimeout(timeout, 60000);
}
timeout();