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Pause and start JS countdown timer

I am trying to develop a centurion countdown timer for my website. It is a drinking game.
The way the timer works is: It is a 60 second countdown timer. Everytime the timer hits 0 it will +1 a shot counter and restart. It will do this 100 times.
The game is you must do 1 shot, every minute for 100 minutes. I am a beginner at JS and I am learning a lot, but I am seriously struggling to get this to work the way I want it to.
All I need is a "Start" Button, a "Pause" button and a "Reset" button but I can't seem to find a way to make these buttons work without messing the timer up.
Here is the HTML code:
<div class="inner">
<h1 class="heading alt">Centurions Timer</h1>
<p>1 Shot. Every Minute. 100 Minutes.</p>
<p>___________________________________</p>
<div id="timer">
<p id="seconds">60</p>
<p id="shots">0</p>
</div>
<input type="button" value="Start" onclick="timer()">
<input type="button" value="Pause" onclick="clearInterval(myTimer)">
</div>
and here is the JS code:
var seconds = 60;
var shots = 0;
var timer;
var c = 60;
function timer() {
timer = setInterval(myTimer, 1000)
}
function myTimer() {
document.getElementById("seconds").innerHTML = --c;
if (c == 0) {
shots = shots + 1;
c = 60;
}
document.getElementById("shots").innerHTML = shots;
}
If anyone could help me and show me what I am doing wrong and how I can make the code better, please do!

First, consider renaming either your method timer() or variable timer to disambiguate between the two.
Next, setInterval() returns an interval ID, which you store in timer.
clearInterval() takes the interval ID as the parameter, so try passing it the timer variable instead of myTimer (a function)

Little bit clean up needed. For clearInterval, u have to id of timer to clear
var seconds = 60;
var shots = 0;
var timer;
var c = 60;
function start() {
clearInterval(timer)
timer = setInterval(( ) =>{
updateUi()
}, 1000);
}
function pause() {
clearInterval(timer)
}
function updateUi() {
document.getElementById("seconds").innerHTML = --c;
if (c == 0) {
shots = shots + 1;
c = 60;
}
document.getElementById("shots").innerHTML = shots;
}
<div class="inner">
<h1 class="heading alt">Centurions Timer</h1>
<p>1 Shot. Every Minute. 100 Minutes.</p>
<p>___________________________________</p>
<div id="timer">
<p id="seconds">60</p>
<p id="shots">0</p>
</div>
<input type="button" value="Start" onclick="start()">
<input type="button" value="Pause" onclick="pause()">
</div>

You can also use Pub Sub model, to make code looks clean.
var seconds = 60;
var shots = 0;
var c = 60;
function Emitter() {
this.cb;
this.on = cb => {
this.cb = cb;
};
this.emit = () => {
this.cb && this.cb();
};
this.cancel = () => {
this.cb = null;
};
}
const emitter = new Emitter();
const tick = () => {
setInterval(() => {
emitter.emit();
}, 1000);
};
tick()
function start() {
emitter.on(updateUi);
}
function pause() {
emitter.cancel();
}
function updateUi() {
document.getElementById("seconds").innerHTML = --c;
if (c == 0) {
shots = shots + 1;
c = 60;
}
document.getElementById("shots").innerHTML = shots;
}
<div class="inner">
<h1 class="heading alt">Centurions Timer</h1>
<p>1 Shot. Every Minute. 100 Minutes.</p>
<p>___________________________________</p>
<div id="timer">
<p id="seconds">60</p>
<p id="shots">0</p>
</div>
<input type="button" value="Start" onclick="start()">
<input type="button" value="Pause" onclick="pause()">
</div>

<div class="inner">
<h1 class="heading alt">Centurions Timer</h1>
<p>1 Shot. Every Minute. 100 Minutes.</p>
<p>___________________________________</p>
<div id="timer">
<p id="minutes">100</p>
<p id="seconds">60</p>
<p id="shots">0</p>
</div>
<input type="button" value="START" onclick="start()">
<input type="button" value="PAUSE" onclick="pause()">
<input type="button" value="RESET" onclick="reset()">
</div>
Changed the onclick functions to something more meaningful. Added an extra button and some more logic to auto-stop when hitting the 100 minutes.
var seconds = 60,
minutes = 100,
shots = 0;
timer = "";
// this will just stop the timer, if you click start it will resume from where it left off
function pause() {
clearInterval(timer);
}
// resets seconds/minutes/shots, stops game
function reset() {
clearInterval(timer);
seconds = 60;
minutes = 100;
shots = 0;
timer = "";
document.getElementById("minutes").innerHTML = minutes;
document.getElementById("seconds").innerHTML = c;
document.getElementById("shots").innerHTML = shots;
}
// starts game from wherever it was left
function start() {
timer = setInterval(function() {
document.getElementById("seconds").innerHTML = c--;
if (c === 0) {
document.getElementById("minutes").innerHTML = --minutes;
// when 100 minutes are up, game will stop and reset
if (minutes === 0) {
reset();
}
shots++;
c = 60;
}
document.getElementById("shots").innerHTML = shots;
}, 1000)
}

How to stop countdown after a few rounds?

var secondsP = document.getElementById('seconds');
var btn1 = document.getElementById("btnSurrender");
var clock = null;
btn1.addEventListener("click", surrender);
function timer () {
clearInterval(clock);
var start = new Date().getTime();
clock = setInterval(function() {
var seconds = Math.round(15 - (new Date().getTime() - start) / 1000);
if (seconds >= 0) {
secondsP.textContent = seconds;
} else {
clearInterval(clock);
}
if (seconds === 0) {
}
}, 1000);
}
function surrender(){
clearInterval(clock);
secondsP.textContent = 0;
setTimeout(timer,2000);
}
timer();
setInterval(timer, 17000);
<html>
<head>
<style>
</style>
<script src="/scripts/snippet-javascript-console.min.js?v=1"></script>
</head>
<body>
<p id="seconds">15</p>
<button id= "btnSurrender">end now</button>
</body>
</html>
I need help with my little problem. I made a stopwatch which counts down 15 seconds. After this 15 seconds, it waits two seconds and starts again. You have option to stop counting when you want to, using "end now" button (then it'll start again after 2 sec). Now, my question is: how can I make a function which is going to stop whole counting after 3/4 rounds?

You restart the clock in surrender() using the call setTimeout(timer, 2000). All you need to do is add an if statement inside that function testing a variable that controls how many times you have run the timer, and then call/not call timer() accordingly. Here is a working example of it: https://jsfiddle.net/L38q6k5d/, but just to give you an idea of how it would work:
At the top of the js file:
var timesRun = 0
var timerInterval = null;
Inside the surrender function:
timesRun += 1 // Increment it each time the timer ends
if (timesRun > 4) { // If the timer has run less than 4 times
return; // this will stop the function here, so we dont start the timer again
}
setTimeout(timer, 2000); // Reset the timer
Inside the timer function,
if (timesRun > 1) {
clearInterval(timerInterval);
return; // end the function here
}
When starting the initial timer:
timer();
timerInterval = setInterval(timer, 17000);
Complete JS:
var secondsP = document.getElementById('seconds');
var btn1 = document.getElementById("btnSurrender");
var clock = null;
var timerInterval = null;
// New Code
var numberOfTimesRun = 0; // this is where we keep track of how many times the timer has run
btn1.addEventListener("click", surrender);
function timer () {
clearInterval(clock);
// New Code
if (numberOfTimesRun > 1) {
clearInterval(timerInterval);
return; // end the function here
}
// End New Code
var start = new Date().getTime();
clock = setInterval(function() {
var seconds = Math.round(15 - (new Date().getTime() - start) / 1000);
if (seconds >= 0) {
secondsP.textContent = seconds;
} else {
clearInterval(clock);
numberOfTimesRun += 1; // so we know that 1 iteration of the timer has been completed
}
if (seconds === 0) {
}
}, 1000);
}
function surrender(){
clearInterval(clock);
secondsP.textContent = 0;
//New Code
numberOfTimesRun += 1;
if (numberOfTimesRun > 4) {
return; // end the function there
}
setTimeout(timer, 2000)
//End New Code
}
timer();
timerInterval = setInterval(timer, 17000);

Re-starting a timer after stopping it

Problem: When I click my start button after stopping my timer, I can't seem to get the timer to resume.
Desired result: For any given timer, when I click the start button, after clicking the stop button, I want the time to resume where it left off.
I figured that when clicking the start button, it would just call the setInterval function again after being cleared, however, I am having issues figuring that out.
I have the stop event in each function in the same scope as the intervalID var's, which hold the setInterval functions itself. Which is why the stop button works. Calling the timer functions(setPomodoro, setLongBreak, setShortBreak) resets their timer's to the original state. I can't seem to grasp how to resume from the timer's time when it's stopped.
JSBIN: http://jsbin.com/bucalequsi/edit?html,js,output
Re-creation:
// Problem: Pomodor timer does not have functionality
// Solution: Add functionality to the pomodor timer.
// IF a break timer is running WHILE another is clicked, stop running timer, start clicked timer.
// Reset current interval time on reset button.
// If break buttons are clicked more than once, reset the time.
window.onload = function() {
var pomodoro = document.querySelector('#set-time'),
longBreak = document.querySelector('#long-brk'),
shortBreak = document.querySelector('#short-brk'),
stopButton = document.querySelector('#stop'),
startButton = document.querySelector('#start'),
resetButton = document.querySelector('#reset'),
container = document.querySelector('#container'),
actionButtons = document.querySelector('#buttons'),
timer = document.querySelector('#timer');
// Click event for break timers.
container.addEventListener('click', function(e) {
// store event target
var el = e.target;
if (el === pomodoro) {
setPomodoro();
} else if (el === longBreak) {
setLongBreak();
} else if (el === shortBreak) {
setShortBreak();
}
e.stopPropagation();
}, false);
// 1.1a Create a timer that counts down from 25 minutes.
function setPomodoro() {
var mins = 24;
var secs = 60;
var intervalID = setInterval(function() { //set unique interval ID for each SI func.
timer.innerHTML = mins + ':' + secs;
secs--;
if (secs === 0) {
mins--;
secs = 60;
}
}, 1000);
// 2.2 When stop button is clicked, timer stops
stopButton.addEventListener('click', function() {
clearInterval(intervalID);
}, false);
}
// 1.2a Create a timer that counts down from 10 minutes
function setLongBreak() {
var mins2 = 9;
var secs2 = 60;
var intervalID2 = setInterval(function() {
timer.innerHTML = mins2 + ':' + secs2;
secs2--;
if (secs2 === 0) {
mins2--;
secs2 = 60;
}
}, 1000);
stopButton.addEventListener('click', function(){
clearInterval(intervalID2);
}, false);
}
// 1.3a Create a timer that counts down from 5 minutes.
function setShortBreak() {
var mins3 = 4;
var secs3 = 60;
var intervalID3 = setInterval(function() {
timer.innerHTML = mins3 + ':' + secs3;
secs3--;
if (secs3 === 0) {
mins3--;
secs3 = 60;
}
}, 1000);
stopButton.addEventListener('click', function() {
clearInterval(intervalID3);
}, false);
}
};
HTML:
<!DOCTYPE html>
<html>
<head>
<title>Pomodoro Timer</title>
<meta charset="utf-8">
<meta name="viewport" content="width=device-width, initial-scale=1">
<link rel="stylesheet" href="normalize.css">
<link rel="stylesheet" href="main.css">
</head>
<body>
<div id="container">
<header>
<div id="header"><h1>Pomodoro Timer</h1></div>
</header>
<div class="row">
<ul id="breaks">
<li><input type="submit" value="Pomodoro" id="set-time"></li>
<li><input type="submit" value="Long Break" id="long-brk"></li>
<li><input type="submit" value="Short Break" id="short-brk"></li>
</ul>
</div>
<h1 id=timer></h1>
<div class="row">
<ul id="buttons">
<li><input type="submit" value="Start" id="start"></li>
<li><input type="submit" value="Stop" id="stop"></li>
<li><input type="submit" value="Reset" id="reset"></li>
</ul>
</div>
<footer>
<p>© Laere 2016</p>
</footer>
</div>
<script src="script.js"></script>
</body>
</html>

When the set... functions are started with the buttons, you always initialise the times to starting values. Instead, if there is a timer already running you have to parse the paused time string into minutes and seconds and use those values to set your vars mins and secs.
Maybe something like this will work?
function setPomodoro() {
if(timer.innerHTML.length > 0){
var t = timer.innerHTML.split(':');
var mins = parseInt(t[0]);
var secs = parseInt(t[1]);
}
else{
var mins = 24;
var secs = 60;
}
var intervalID = setInterval(function() { //set unique interval ID for each SI func.
timer.innerHTML = mins + ':' + secs;
secs--;
if (secs === 0) {
mins--;
secs = 60;
}
}, 1000);
// 2.2 When stop button is clicked, timer stops
stopButton.addEventListener('click', function() {
clearInterval(intervalID);
}, false);
}

Javascript Second into Minutes:Seconds

I am working on a clock that needs to display seconds into a
minutes:seconds
format.
I have worked on some auxiliary functions for display, but I have never really gotten the full display. Here is some of my code:
var time = 1500;
//Must declare timeHandler as global variable for stopTimer()
var timeHandler;
//Set intial HTML to time
document.getElementById("timer").innerHTML = display;
//Timer function for start button
function timer() {
timeHandler = setInterval(function() {
if (time > 0) {
time--;
document.getElementById("timer").innerHTML = time;
}
}, 1000);
}
//Stop function for stop button
function stopTimer() {
clearTimeout(timeHandler);
}
//Timer Display
var minutes = time/60;
var second = time%60;
var display = minutes + ":" + seconds;
HTML:
<h1> Pomodoro Clock</h1>
<!--Place holder for timer-->
<div id="timer" class="circle">Timer</div>
<!--//Start Button-->
<button onclick="setTimeout(timer, 1000);">Start</button>
<!--Stop Button-->
<button onclick="stopTimer()">Stop</button>

Thie formatTime function below will take a number of seconds, and convert it to MM:SS format (including padded zeroes):
var time = 1500;
//Must declare timeHandler as global variable for stopTimer()
var timeHandler;
//Set intial HTML to time
document.getElementById("timer").innerHTML = display;
//Timer function for start button
function timer() {
timeHandler = setInterval(function() {
if (time > 0) {
time--;
document.getElementById("timer").innerHTML = formatTime(time);
}
}, 1000);
}
//Stop function for stop button
function stopTimer() {
clearTimeout(timeHandler);
}
function formatTime(seconds) {
//Timer Display
var minutes = seconds / 60;
var second = seconds % 60;
return ('0'+minutes).substr(-2) +":"+ ('0'+seconds).substr(-2);
}

first of all you have to use clearInterval, then you don't update your display every second
check this fiddle out

How would I find the difference between two button clicks in milliseconds?

I'm trying to make a program that tests your reaction time, but I don't know how to measure the time between two events, like button clicks. Here's my code so far. Thanks in advance to anyone that can help.
<!DOCTPYE html>
<html>
<head>
<script>
var button = document.getElementById("reactionTester");
var start = document.getElementById("start");
function init() {
var startInterval/*in milliseconds*/ = Math.floor(Math.random() * 30) * 1000;
setTimeout(startTimer, startInterval);
}
function startTimer() {
/*start timer and then later use stopTimer() to stop the timer and find
the difference bettween both button clicks.*/
}
</script>
</head>
<body>
<form id="form">
<input type="button" id="reactionTester" onclick="stopTimer()">
<input type="button" value="start" id="start" onclick="init()">
</form>
</body>
</html>

var startTime;
function startButton() {
startTime = Date.now();
}
function stopButton() {
if (startTime) {
var endTime = Date.now();
var difference = endTime - startTime;
alert('Reaction time: ' + difference + ' ms');
startTime = null;
} else {
alert('Click the Start button first');
}
}
Bind your start and stop buttons to these functions.
DEMO

For getting the time that has passed, you'll always need a start_time and end_time. startTimer() should set a start_time variable (or something similarly named), and stopTimer() should set an end_time variable.
stopTimer() can then subtract the two times and you've got the number of milliseconds passed.
(JavaScript stores times in milliseconds, so oldTime - newTime = milliseconds passed.)
Edit: Example JSFiddle - http://jsfiddle.net/L3Xha/
var startTime, endTime;
// self-executing function
(function(){
// init the background to white
document.body.style.background = "white";
// reset the color of the BG after 3 seconds.
setTimeout(
function(){
document.body.style.background = "red";
startTime = Date.now();
}
, 3000);
$("#go").on("click", function(){
stopTime = Date.now();
$("#reflex").text(
"Your time was " + (stopTime - startTime) + "ms."
);
});
})();

Keep track of the time of the first click, and on the second click, display the difference between now and the first click.
var start;
$('button').click(function() {
if (undefined === start) {
start = new Date().getTime();
return;
}
alert('Time difference is:' + (new Date.getTime() - start));
});

To measure millseconds between two button clicks, log timestamps in javascript
First Button:
document.getElementById('submit-button1').onclick = function() {
console.log(new Date().getTime()); //1388696290801
}
Second Button:
document.getElementById('submit-button2').onclick = function() {
console.log(new Date().getTime()); //1388696292730
}

You don't need a form, you just need buttons, you don't need intervals either. You also don't need jQuery.
<!DOCTPYE html>
<html>
<head>
<script>
var startTime, running;
function startStop() {
if (running) {
var timeTaken = Date.now() - startTime;
running = false;
console.log("Time: " + timeTaken);
}
else {
running = true;
startTime = Date.now();
}
}
</script>
</head>
<body>
<button onclick="startStop();">Start/Stop</button>
</body>
</html>
Edit
Date.now() is probably faster.