How can I make 2 counters running back to back with javascript? - javascript

The following function naturally enters the same loop over and over again. What I want to do is start counting down from 25 seconds, when it's finished, start counting down from 10 seconds, then go back to 25 seconds. But because of the condition I wrote in the else part, it always counts backwards from 10 seconds. How can I fix this?
var interval = 25000;
var interval1 = 10000;
function millisToMinutesAndSeconds(millis) {
var seconds = ((millis % 60000) / 1000).toFixed(0);
return (seconds < 10 ? "0" : "") + seconds;
}
function tensecond() {
localStorage.endTime = +new Date() + interval1;
}
function reset() {
localStorage.endTime = +new Date() + interval;
}
setInterval(function () {
var remaining = localStorage.endTime - new Date();
if (remaining >= 0) {
document.getElementById("timer").innerText =
millisToMinutesAndSeconds(remaining);
} else {
tensecond();
}
}, 100);

Some comments:
Don't use the localStorage object to store your own properties. This has nothing to do with the purpose of localStorage. Just use a global variable (if you need local storage, then use its getItem and setItem methods)
Don't use toFixed(0) to round a number to an integer. Moreover, the comparison of that string with 10 will make a character-based comparison, not a numerical comparison. Instead use Math.round, or more appropriate here: Math.floor.
Don't use new Date() when you want a number of milliseconds instead of a Date object. Use Date.now() instead.
Don't do arithmetic on values that are not initialised. Initialise endTime before starting any logic on it. So call reset() before calling setInterval()
As to your question:
One way to get this to work is to make a cycle that covers both intervals added together. Then at each tick check whether the remaining time falls inside the first or second interval. Adjust the displayed remaining time accordingly.
Here is how that looks:
var interval = 25000;
var interval1 = 10000;
var endTime;
function millisToMinutesAndSeconds(millis) {
// Use floor instead of toFixed
var seconds = Math.floor((millis % 60000) / 1000);
return (seconds < 10 ? "0" : "") + seconds;
}
function reset() {
// Use Date.now() instead of +new Date()
// And create a cycle length that covers both intervals
endTime = Date.now() + interval + interval1;
}
reset();
setInterval(function () {
var remaining = endTime - Date.now();
if (remaining >= 0) {
// Adjust the time to display
// depending on where in the total interval we are:
if (remaining >= interval1) remaining -= interval1;
document.getElementById("timer").innerText =
millisToMinutesAndSeconds(remaining);
} else {
reset()
}
}, 100);
<div id="timer"></div>

There's no need to incorporate specific datetimes or local storage if you just need an alternating countdown timer. A simpler technique is to just keep track of the number of remaining seconds and do updates after a repeated 1s delay, subtracting a second from the total each time.
Here's an example of that (and it also displays each second rounded up instead of rounded down — so it starts with 25 (or 10) and resets at the exact moment that 0 is reached rather than displaying 0 for an entire second):
const timerElement = document.getElementById('timer');
function updateTimerElement (seconds) {
timerElement.textContent = String(seconds).padStart(2, '0');
}
function delay (ms) {
return new Promise(resolve => setTimeout(resolve, ms));
}
async function countdown (seconds) {
while (seconds > 0) {
updateTimerElement(seconds);
await delay(1e3); // 1e3 is 1000 (1s)
seconds -= 1;
}
// You might want to update the timer one final time in order to show 0
// if you ever stop looping the countdowns:
// updateTimerElement(seconds);
}
async function main () {
// Store the total number of seconds for each countdown in order:
const secondsList = [25, 10];
// Keep track of the current one:
let listIndex = 0;
while (true) {
// Get the current number of seconds from the list:
const seconds = secondsList[listIndex];
// Run the countdown timer:
await countdown(seconds);
// Update the index to the next number of seconds in the list:
listIndex = (listIndex + 1) % secondsList.length;
}
}
main();
body { font-family: sans-serif; font-size: 4rem; }
<div id="timer"></div>
Finally, take care to note that JavaScript timers are not precise timing tools. See more info at: Reasons for delays longer than specified - setTimeout() - Web APIs | MDN

These are the facts:
The first time the (anonymous) interval function runs, localStorage.endTime isn't initialized, so has value undefined.
Any arithmetic operations on undefined result in NaN1, 2, 3, so remaining is initialized to NaN.
Any comparisons to NaN (other than != and !==) are false4, 5, 6, so the first time the interval function runs, it calls tensecond.
Thereafter, the interval function counts down. When the timer runs out, it again calls tensecond.
Short version: reset is never called.
ECMAScript, 13th Ed references
§ 13.15.3 ApplyStringOrNumericBinaryOperator
§ 7.1.4 ToNumber
§ 6.1.6.1.7 Number::add ( x, y )
§ 13.11.1 Runtime Semantics: Evaluation
§ 7.2.15 IsLooselyEqual ( x, y )
6.1.6.1.13 Number::equal

Related

How can I send messages at regular intervals? [duplicate]

I am trying to update information from a weather service on my page. The info should be updated every hour on the hour. How exactly do I go about calling a function on the hour every hour?
I kind of had an idea but I'm not sure of how to actually refine it so it works...
What I had in mind was something like creating an if statement, such as: (pseudo code)
//get the mins of the current time
var mins = datetime.mins();
if(mins == "00"){
function();
}
You want to check out setInterval: https://developer.mozilla.org/en-US/docs/Web/API/Window.setInterval
It's a little hard to tell what you're trying to call with your code, but it would be something in the form of:
function callEveryHour() {
setInterval(yourFunction, 1000 * 60 * 60);
}
If you want it every hour, try something like:
var nextDate = new Date();
if (nextDate.getMinutes() === 0) { // You can check for seconds here too
callEveryHour()
} else {
nextDate.setHours(nextDate.getHours() + 1);
nextDate.setMinutes(0);
nextDate.setSeconds(0);// I wouldn't do milliseconds too ;)
var difference = nextDate - new Date();
setTimeout(callEveryHour, difference);
}
Now, this implementation checks the time once, sets the delay (or calls the function immediately), and then relies on setInterval to keep track after that. An alternative approach may be to poll the time every x many seconds/minutes, and fire it .getMinutes() == 0 instead (similar to the first part of the if-statement), which may sacrifice (marginal) performance for (marginal) accuracy. Depending on your exact needs, I would play around with both solutions.
Here is what should work (JSFiddle):
function tick() {
//get the mins of the current time
var mins = new Date().getMinutes();
if (mins == "00") {
alert('Do stuff');
}
console.log('Tick ' + mins);
}
setInterval(tick, 1000);
What you probably want is something like that:
var now = new Date();
var delay = 60 * 60 * 1000; // 1 hour in msec
var start = delay - (now.getMinutes() * 60 + now.getSeconds()) * 1000 + now.getMilliseconds();
setTimeout(function doSomething() {
// do the operation
// ... your code here...
// schedule the next tick
setTimeout(doSomething, delay);
}, start);
So basically the first time the user get the access, you need to know what is the delay in millisecond to the next "hour". So, if the user access to the page at 8:54 (with 56 seconds and 123 milliseconds), you have to schedule the first execution after around 3 minutes: after the first one is done, you can call it every "hour" (60 * 60 * 1000).
Repeat at specific minute past the hour
This counter is a little bit more versatile; it allows to perform a task repeatedly always at the same minute past the hour (e.g. 37 minutes past the hour), and this with up to millisecond precision.
The precision of this timer is derived from its recursion.
At every recursion, the millisecond time to the next minute gets recalculated. This prevents time lag over long periods.
The % sign refers to the modulo operator.
function minuteCount(minutesAfterHour) {
const now = new Date();
const hours = now.getHours();
const minutes = now.getMinutes();
const seconds = now.getSeconds();
const milliseconds = now.getMilliseconds();
waitUntilNextMinute = setTimeout(minuteCount, 60000 - seconds * 1000 - milliseconds);
if(minutes % 60 === minutesAfterHour) {
doSomethingHourly();
}
}
minuteCount(37);
Finally, timers are best kept away from the main thread. They are best run from within a web worker, as explained here.
This works perfectly with unfocused tabs in desktop browsers.
However, dedicated web workers on Chrome for Android are put to sleep about 5 minutes after moving the main client to the background.
EDIT: Oops, I didn't see the " o' clock" things, so I edit my answer :
var last_execution = new Date().getTime();
function doSomething(force){
var current_time = new Date().getTime();
if (force || (current_time.getMinutes() == 0)
{
last_execution = current_time;
// something
// ...
}
setTimeout(doSomething(false), 1000);
}
// force the first time
doSomething(true);
// ... call your func now
let intervalId;
let timeoutId = setTimeout(() => {
// ... call your func on end of current hour
intervalId = setInterval(() => {
// ... call your func on end of each next hours
}, 3600000);
}, ((60 − moment().minutes()) × 60 × 1000) - (moment().second() * 1000));
Here is my pair of setIntervalWithDelay and clearIntervalWithDelay that one can use like this:
let descriptor = setIntervalWithDelay(callback, 60 * 60 * 1000, nextHourDelay)
And when you are done with it:
clearIntervalWithDelay(descriptor)
Here is my implementation of the functions:
const setIntervalWithDelay = (callback, interval, delay = 0) => {
let descriptor = {}
descriptor.timeoutId = setTimeout(() => {
if(!descriptor.timeoutId){
return
}
descriptor.timeoutId = null
callback()
descriptor.intervalId = setInterval(callback, interval)
}, delay)
return descriptor
}
export const clearIntervalWithDelay = (descriptor) => {
if(!isObject(descriptor) || (!descriptor.timeoutId && !descriptor.intervalId)){
console.warn("clearIntervalWithDelay: Incorrect descriptor. Please pass an object returned by setIntervalWithDelay. Skipping this call.")
return
}
if(descriptor.timeoutId){
clearTimeout(descriptor.timeoutId)
descriptor.timeoutId = null
console.log("clearIntervalWithDelay: stopped during delay.")
}
if(descriptor.intervalId){
clearInterval(descriptor.intervalId)
descriptor.intervalId = null
console.log("clearIntervalWithDelay: stopped during interval repeat.")
}
}
One example of using dayjs to get the delay for the next hour:
let nextHour = dayjs().second(0).millisecond(0).add(1, "hour")
let nextHourDelay = nextHour.diff(dayjs())

Javascript timer using setInterval() onclick and add duration, if a condition is satisfied

var score = 0,
time = 10;
window.onload = function() {
var input = document.getElementById("wordTyped");
var timeLeft = document.getElementById("time");
input.addEventListener("click", timer, false);
function timer() {
var id = setInterval(countdown, 10);
function countdown() {
input.removeEventListener("click", timer, false);
timeLeft.innerHTML = "Time left: " + (time - 0.01).toFixed(2) + "s";
time = (time - 0.01).toFixed(2);
if (time == 0) {
clearInterval(id);
}
if (time == 7) {
// The issue | it works if I assigned 10 to time but not for addition"
time += 10;
}
}
}
}
<input id="wordTyped" type="text" />
<div id="time">Time left: 10.00s</div>
The code I wrote above is fairly straight forward but its not working the way I'm expecting it to work.
If input is clicked, start timer and if time == 7 (for testing sake, I give the condition for time equals 7), add 10 to time but it doesn't add and keeps on decrementing until it reach zero where the setInterval is cleared
Don't use toFixed() when assigning to time. That returns a string, not a number, so time += 10 performs string concatenation, not addition. Use it only when displaying the time, not storing the time variable in the code.
However, if you keep time as a number, floating point inaccuracies may result in time == 7 never being true. You should test for it being close to 7:
if (Math.abs(time - 7) < 0.005)
#epascarello, thanks for clarifying, wish I can upvote your comment.
If toFixed() set it into a string, then all that needs to be done is to revert it back into a number type.
So I change
time = (time - 0.01).toFixed(2);
into
time = 1 * (time - 0.01).toFixed(2);

Javascript: restarting countdown timer doesn't work as I expect it to

I am making a countdown timer that should be reseting and starting anew every 10 seconds.
This is the code I came up with by now:
function count(){
var end_date = new Date().getTime()+10*1000;
setInterval(function(){
var current_date = new Date().getTime();
var seconds_left = parseInt((end_date - current_date) / 1000);
document.getElementById("countdown").innerHTML = seconds_left + " seconds ";
}, 1000);
}
setInterval(function(){count()}, 10*1000);
It is supposed to function as follows:
+ I set interval that will restart count() every 10 seconds.
+ count() defines end_date - a date 10 seconds from now.
+ then count() sets interval that will restart every 1 second.
+ every 1 second seconds_left variable is changed according to how current_date changed with respect to end_date.
+ as soon as seconds_left becomes 0, setInterval from step 1 fires and starts count() anew.
Which step am I implementing the wrong way? Do I misunderstand the functioning of setInterval()?
Here is my JsFiddle: http://jsfiddle.net/sy5stjun/ .
My guess is that each call is in its own new object and you get multiple instances of itself fighting ever 10 seconds.
Using your approach using date objects here is a possible re-write:
var tmr = null;
var time;
function bigInterval() {
clearInterval(tmr);
time = (new Date()).valueOf() + (10 * 1000);
smallInterval();
tmr = setInterval(smallInterval, 500);
}
function smallInterval() {
var cur = (new Date()).valueOf();
var seconds_left = parseInt((time - cur) / 1000);
document.getElementById("countdown").innerHTML = seconds_left + " seconds";
}
bigInterval();
setInterval(bigInterval, 10*1000);
In the above code I've updated the small timer to be 500ms instead of 1000ms as it won't exactly line up with the system clock at 1000 and you get visual jumps in the numbers.
If exact timing isn't 100% important then here is a possible shorter method:
var t = 10;
setInterval(function() {
document.getElementById("countdown").innerHTML = t + " seconds";
t--;
if (t <= 0) {
t = 10;
}
}, 1000);
There are a few things going on, here. You're not specific why you have to set another interval inside your loop, but there are a lot easier ways to accomplish what you're going for. Another approach follows:
HTML:
<!-- string concatenation is expensive in any language.
Only update what has to change to optimize -->
<h1 id='countdown'><span id="ct"></span> seconds </h1>
JS:
// For one thing, grabbing a new reference to the
// dom object each interval is wasteful, and could interfere with
// timing, so get it outside your timer, and store it in a var scoped
// appropriately.
var ct = document.getElementById("ct");
// set your start
var ctStart = 10;
// set your counter to the start
var ctDown = ctStart;
var count = function() {
// decrement your counter
ctDown = ctDown - 1;
// update the DOM
ct.innerHTML = ctDown;
// if you get to 0, reset your counter
if(ctDown == 0) { ctDown = ctStart; }
};
// save a reference to the interval, in case you need to cancel it
// Also, you only need to include a reference to the function you're
// trying to call, here. You don't need to wrap it in an anonymous function
var timer = window.setInterval(count, 1000);
My jsFiddle available for tinkering, here: http://jsfiddle.net/21d7rf6s/

Run javascript for X amount of minutes

i am trying to create a program that will run for X amount of minutes.
minutes was always set to 1 in testing
var minutes = $('#minutes').val();
var runtime = minutes*60; // gets the seconds
var secondsEpoch = new Date() / 1000; // Epoch time
var End = secondsEpoch + runtime; // add the minutes to the current epoch
if (secondsEpoch < End) {
window.setInterval(RunClock, 1000/10);
} else {
clearInterval(RunClock);
}
function RunClock() {
console.log(new Date() / 1000);
//my code
}
The script runs for infinity and i'm confused on why ???
When alerting variable secondsEpoch and End i always end up with a time difference of 1 minute?
Alerted the start and finish times and got
Start 1395022190.621
Finish 1395022250.621
Total difference of 60 which = 1 minute
but the console log at this minute is
1395022456.657
which is obviously greater than
1395022250.621
and the scrip is still running and not stopping
You are not clearing your interval correctly. This way it will work:
var interval;
if (secondsEpoch < End) {
interval = setInterval(RunClock, 1000/10);
} else {
clearInterval(interval);
}

A Better (Hopefully) JavaScript Countdown Timer

In our application, we have a need for a robust countdown timer. When the timer counts down to zero, we move the user on to the next page.
There are a LOT of questions on here about making a countdown timer in JavaScript. I've weeded through a lot of them, looked at a lot of the code samples, tried a lot of plugins, and all of them fail for this one test case: If you adjust your computers system clock, all of these timers mess up (gain time, lose time, or just freeze). The reason is that most of them base their logic on saving some initial start time and then at some interval (either via setTimeout or setInterval) getting the current time and doing a diff between it and the start time. When you adjust your system time, the "current" time can be an hour or days before your start time, or hours or days later.
So, I've come up with the following code to try to handle these system change scenarios. The main thing I do is check if the "diff" between my start and current is negative (or greater than roughly one hour to handle an automatic daylight savings adjustment) to just use the tick interval as an approximation. Also, reset the start time to be current time on each tick, so that elapsed time is the sum of the time between differences, not just the diff between an initial start time and current time. Anyone see any flaws with this approach?
var timeLeft = 60000, // time left in ms, 1 minute for this example
startTime,
totalElapsedTime = 0,
TICK_INTERVAL = 500; // the setTimeout interval
var timerTick = function () {
var now = new Date(),
elapsedTime = now.getTime() - startTime.getTime();
// if the elapsed time was positive and less than approximately an hour, then add the elapsed time to the total
// otherwise, add the TICK_INTERVAL, which we know is the theoretical minimum between timerTick() calls
totalElapsedTime = (elapsedTime > 0 && elapsedTime < 3590000) ? totalElapsedTime + elapsedTime : totalElapsedTime + TICK_INTERVAL;
// reset start time
startTime = now;
// there is time left, so set up another tick
if (totalElapsedTime < timeLeft) {
// update the html that is displaying remaining time
setTimeout(timerTick, TICK_INTERVAL);
}
else {
// time ran out, so do whatever you do when it runs out
}
}
// start the timer
startTime = new Date();
setTimeout(timerTick, TICK_INTERVAL);
Why does the following not work for you?
var timeleft = 60000,
tick = 1000,
intervalID = window.setInterval(function () {
timeleft = timeleft - tick;
if (timeleft <= 0) {
// clear the interval
clearInterval(intervalID);
// do something
}
}, tick);
Update
Using setTimeout (this will drift, but probably be ok unless you are using it for animation):
var timeleft = 60000,
tick = 1000;
window.setTimeout(function timerFn() {
timeleft = timeleft - tick;
if (timeleft > 0) {
// set the next timeout
setTimeout(timerFn, tick);
} else {
// do something
}
}, tick);

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