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Restart Timer Using Javascript

I try to use JavaScript to set timer for my quiz.(setInterval) but if I finish the quiz earlier and click on start button gain, the time will start counting at the time I stop the quiz. How can I restart the time after I click on the start button again? .
<script>
var seconds = 40;
if (localStorage.getItem("counter")) {
if (localStorage.getItem("counter") <= 0) {
var value = seconds;
alert(value);
} else {
var value = localStorage.getItem("counter");
}
} else {
var value = seconds;
}
document.getElementById("divCounter").innerHTML = value;
var counter = function() {
if (value <= 0) {
localStorage.setItem("counter", seconds);
value = seconds;
} else {
value = parseInt(value) - 1;
localStorage.setItem("counter", value);
}
document.getElementById("divCounter").innerHTML = value;
};
var interval = setInterval(function() { counter(); }, 1000);
</script>

Based on your current code what you need to do to reset the counter is set value=seconds and removing the current value in localStorage.
So assuming you have a button like this in your HTML:
<button type"button" onclick="resetCounter()">Reset</button>
you can add a resetCounter() function in your code:
var resetCounter = () => {
value = seconds;
localStorage.removeItem("counter");
};

Starting timer when clicking first card of memory game

Ok I am trying to wrap up a project and the only thing holding me back is it that they call for the timer to start on clicking a match game. The timer starts when the HTML file loads which is not what the project wants and I have tried some methods but ends up freezing the game. I want the timer to be able to start when clicking a card.
var open = [];
var matched = 0;
var moveCounter = 0;
var numStars = 3;
var timer = {
seconds: 0,
minutes: 0,
clearTime: -1
};
//Start timer
var startTimer = function () {
if (timer.seconds === 59) {
timer.minutes++;
timer.seconds = 0;
} else {
timer.seconds++;
};
// Ensure that single digit seconds are preceded with a 0
var formattedSec = "0";
if (timer.seconds < 10) {
formattedSec += timer.seconds
} else {
formattedSec = String(timer.seconds);
}
var time = String(timer.minutes) + ":" + formattedSec;
$(".timer").text(time);
};
This is the code for clicking on a card. I have tried to include a startTimer code into this but doesn't work.
var onClick = function() {
if (isValid( $(this) )) {
if (open.length === 0) {
openCard( $(this) );
} else if (open.length === 1) {
openCard( $(this) );
moveCounter++;
updateMoveCounter();
if (checkMatch()) {
setTimeout(setMatch, 300);
} else {
setTimeout(resetOpen, 700);
}
}
}
};
And this class code I use for my HTML file
<span class="timer">0:00</span>

Try this: https://codepen.io/anon/pen/boWQbe
All you needed to do was remove resetTimer() call from the function that happens on page load and then just do a check in the onClick (of card) to see if the timer has started yet. timer.seconds == 0 && timer.minutes == 0.

Javascript Countdown Timer Repeat and Count total that repeat

I have javascript countdown timer from 25 -> 0.
var count=25;
var counter=setInterval(timer, 1000); //1000 will run it every 1 second
function timer()
{
count=count-1;
if (count <= 0)
{
clearInterval(counter);
return;
}
document.getElementById("timer").innerHTML=count; // watch for spelling
}
div HTML
<span id="timer">25</span>
Now I want the countdown is repeat automatically after wait 5 seconds then it start again from 25 -> 0. And I want to count how many times that countdown repeat. Is it possible for that?
Please help.

You can try wrapping the entire code into a function (countTimers() in the example below) that runs every 30 seconds (5 seconds after each timer). Then, set a counter (timersCount in the example below) to count how many times that will run.
See the example below:
var timersCount = 0, stopped = false, count, counter; // make count, counter global variables so buttons can access them
var timerCounter = setInterval(countTimers, 30000);
countTimers(); // run countTimers once to start
function timer() {
count = count-1;
document.getElementById("timer").innerHTML=count;
if(count <= 0) {
clearInterval(counter);
return;
}
}
function countTimers() {
timersCount++;
// as per request in the comments, you can set a timer counter as well:
document.getElementById("totalcounter").innerHTML = timersCount;
count = 25;
counter = setInterval(timer, 1000);
}
// button code:
document.getElementById("reset").addEventListener("click", function() {
clearInterval(timerCounter);
clearInterval(counter);
count = 25;
document.getElementById("timer").innerHTML=count;
timersCount = 0;
document.getElementById("totalcounter").innerHTML = timersCount;
stopped = true;
});
document.getElementById("stop").addEventListener("click", function() {
if(stopped)
return;
clearInterval(counter);
stopped = true;
});
document.getElementById("start").addEventListener("click", function() {
if(!stopped)
return;
stopped = false;
counter = setInterval(timer, 1000);
setTimeout(function() {
clearInterval(counter);
timerCounter = setInterval(countTimers, 30000);
countTimers();
}, count*1000);
});
Timer: <span id="timer">25</span><br>
Number of times run: <span id="totalcounter">1</span>
<br><br>
<button id="reset">Reset</button>
<button id="stop">Stop</button>
<button id="start">Start (if stopped)</button>

var count=25;
var counter = null;
// reset count and timer
function reset_timer()
{
count = 25;
counter=setInterval(timer, 1000); //1000 will run it every 1 second
}
// init timer for first time
reset_timer();
function timer()
{
count--;
if (count <= 0)
{
clearInterval(counter);
setTimeout(reset_timer, 5000);
return;
}
document.getElementById("timer").innerHTML=count; // watch for spelling
}
setTimeout is a timer that runs one time and stop.

This approach uses Promises to the countdown work and generate an infinite loop,
if for some reason you need to stop/resume your counter you can reject the Promise chain and have a boolean to control the state:
let secondsCounter =
document.querySelector('#secondsCounter'),
totalCount =
document.querySelector('#totalCount'),
ttc = 1,
actualSecond = 25,
isPaused = false,
interval;
let countDown = time => new Promise( (rs, rj) => interval = setInterval( ()=>{
if (isPaused) {
return rj('Paused');
}
secondsCounter.textContent = --actualSecond;
if (actualSecond == 0){
actualSecond = time + 1;
clearInterval(interval);
rs();
}
}, 1000));
let loop = time => countDown(time).then( ()=>{
totalCount.textContent = ++ttc;
return Promise.resolve(null);
});
let infinite = () => loop(25)
.then(infinite)
.catch(console.log.bind(console));
let stop = () => {
clearInterval(interval);
isPaused = true;
}
let resume = () => {
console.log('Resumed');
isPaused = false;
loop(actualSecond).then(infinite);
}
let start_stop = () => isPaused ?
resume() : stop();
infinite();
Seconds : <div id="secondsCounter">25</div>
Times : <div id="totalCount">1</div>
<button onclick="start_stop()">Start/Stop</button>

How to change the speed of setInterval in real time

I would like to know how to change the speed of setInterval in real time e.g:
if (score < 10)
repeater = setInterval(function() {
spawnEnemy();
}, 1000);
if (score => 10)
repeater = setInterval(function() {
spawnEnemy();
}, 500);
I know this method doesn't work, but is there a way that I can achieve this some other way?

jsFiddle Demo
There is no way to change the interval speed itself once running. The only way to do it is to have a variable for the speed, and then clear the interval and start a new one with the new speed.
var speed = 500;
var changeSpeed = speed;
repeater = setInterval(repeaterFn, speed);
function repeaterFn(){
spawnEnemy();
if( changeSpeed != speed ){
clearInterval(repeater);
speed = changeSpeed;
repeater = setInterval(repeaterFn, speed);
}
}
function changeRepeater(){
changeSpeed = 700;
}

Another way would be to just use setTimeout rather than setInterval. Do the check every time so you can keep your speed logic in a seperate function.
var game_over = false;
var score = 0;
function getSpeedFromScore(score)
{
if (score > 20) {
game_over = true;
}
if (score < 10) {
return 1000;
} else {
return 500;
}
}
function spawnEnemyThenWait() {
if (!game_over) {
spawnEnemy();
var speed = getSpeedFromScore(score);
setTimeout(spawnEnemyThenWait, speed);
}
}
JS Fiddle http://jsfiddle.net/bq926xz6/

You can use clearInterval:
if (score < 10) {
clearInterval(repeater);
repeater = setInterval(spawnEnemy, 1000);
}
if (score => 10) {
clearInterval(repeater);
repeater = setInterval(spawnEnemy, 500);
}
But it depends on the context. If this snippet is executed more often, than it has to be, you will need some kind of mechanism to prevent it from resetting your interval all the time.
But there is (as I wrote in the comment to the question) no way to use clearInterval and change the interval itself. At least not without replacing it by a new interval as shown above.

You can use a game loop and track the spawn state in an enemy class:
// press f12 so see console
function Enemy() {
this.spawned = false;
this.spawnOn = 20;
this.tick = function () {
this.spawnOn = this.spawnOn - 1;
if (this.spawnOn == 0) {
this.spawned = true;
}
}
this.goBackToYourCage = function () {
this.spawnOn = Math.floor(Math.random() * 50) + 1;
this.spawned = false;
}
}
var enemy = new Enemy();
window.setInterval(function () {
enemy.tick();
if (enemy.spawned) {
console.log('spawned');
enemy.goBackToYourCage();
console.log('Next spawin in :' + enemy.spawnOn);
}
}, 100);
http://jsfiddle.net/martijn/qxt2fe8y/2/

Autostart jQuery slider

I'm using a script that animates on click left or right to the next div. It currently works fine but I'm looking to add two features to it. I need it to repeat back to the first slide if it is clicked passed the last slide and go to the last slide if click back from the first slide. Also, I'm interested in getting this to autostart on page load.
I've tried wrapping the clicks in a function and setting a setTimeout but it didn't seem to work. The animation is currently using CSS.
Here's the current JS:
<script>
jQuery(document).ready(function() {
var boxes = jQuery(".box").get(),
current = 0;
jQuery('.right').click(function () {
if (current == (-boxes.length + 1)){
} else {
current--;
updateBoxes();
}
console.log(-boxes.length + 1);
console.log(current);
});
jQuery('.left').click(function () {
if (current === 0){
} else{
current++;
updateBoxes();
}
});
function updateBoxes() {
for (var i = current; i < (boxes.length + current); i++) {
boxes[i - current].style.left = (i * 100 + 50) + "%";
}
}
});
</script>
Let me know if I need a jsfiddle for a better representation. So far, I think the code is pretty straightforward to animate on click.
Thanks.

Try
jQuery(document).ready(function () {
var boxes = jQuery(".box").get(),
current = 0,
timer;
jQuery('.right').click(function () {
if (current == (-boxes.length + 1)) {
current = 0;
} else {
current--;
}
updateBoxes();
}).click(); //initialize the view
jQuery('.left').click(function () {
if (current === 0) {
current = -boxes.length + 1;
} else {
current++;
}
updateBoxes();
});
function updateBoxes() {
//custom implementation for testing
console.log('show', current)
$(boxes).hide().eq(-current).show();
autoPlay();
}
function autoPlay() {
clearTimeout(timer);
//auto play
timer = setTimeout(function () {
jQuery('.right').click();
}, 2500)
}
});
Demo: Fiddle

Here's an example based on my comment (mostly pseudocode):
$(function(){
var boxes = $('.box'),
current = 0,
timer;
// Handler responsible for animation, either from clicking or Interval
function animation(direction){
if (direction === 1) {
// Set animation properties to animate forward
} else {
// Set animation properties to animate backwards
}
if (current === 0 || current === boxes.length) {
// Adjust for first/last
}
// Handle animation here
}
// Sets/Clears interval
// Useful if you want to reset the timer when a user clicks forward/back (or "pause")
function setAutoSlider(set, duration) {
var dur = duration || 2000;
if (set === 1) {
timer = setInterval(function(){
animation(1);
}, dur);
} else {
clearInterval(timer)
}
}
// Bind click events on arrows
// We use jQuery's event binding to pass the data 0 or 1 to our handler
$('.right').on('click', 1, function(e){animation(e.data)});
$('.left').on('click', 0, function(e){animation(e.data)});
// Kick off animated slider
setAutoSlider(1, 2000);
Have fun! If you have any questions, feel free to ask!