Javascript - generate value from time (ms) - javascript

I need to generate some values on Javascript, by clicking on a button, that can't be the same of previous values. I think to generate it from time in ms (in fact I think nobody can't click a button faster than a ms, right?).
What do you think? And how can I do this?

This should do the trick:
new Date().getTime()

yes, I think its pretty solid to use complete datetime (including milliseconds) as a seed for generating a random number.
var currentTime = new Date(),
time = currentTime.getTime();
Check out related question:
Seedable JavaScript random number generator
Also, see David Bau's blog for more information on seeding:
http://davidbau.com/archives/2010/01/30/random_seeds_coded_hints_and_quintillions.html#more

Related

Best javascript/ts approach for finding time till the next [day of week],[HH:mm]

I have been tasked with creating a clientside countdown timer for a list of records. Each record has a value like I specified in the title (Example: Tuesday,05:00). I need to show a running countdown on each row in an Angular 4 application so that if the current time was the day before at 02:30, the value would display as '1d 2h 30m'. I am currently having a total block on how to get started and would appreciate any feedback for turning the next instance of 'Tuesday,05:00' into a usable date/time value to work with.
MomentJs + coundown plugin + (optionaly natives support for momentjs)
As simple as 1 liner:
console.log(moment("1982-5-25").countdown().toString());
For non-english find your desired moment locale.
There couldn't be possibly a simpler and more quality solution that one can write in the 5 min time it takes you to setup this.

Milliseconds out of sync

I am developing a stopwatch application using Javascript/jQuery. The problem is that the milliseconds value is out of sync with REAL milliseconds. I am using function setInterval() with the interval of 1 millisecond, still it is causing this problem.
jsFiddle: http://jsfiddle.net/FLv3s/
Please help!
Use setInterval to trigger updates, but use the system time (via new Date()) for the actual time calculations.
To be honest, I tried nearly the same thing as you do now (Creating an accurate Metronome in Javascript only) - to make a long story short: To be absolutely accurate in terms of milliseconds (or lower) is sadly not (yet) possible with javascript only.
For more insight i recommend this question: Does JavaScript provide a high resolution timer?
or to be more precise this blog article: http://ejohn.org/blog/how-javascript-timers-work/
Best regards,
Dominik
Program execution in any language, not just JavaScript, is not realtime. It will take a tiny amount of time to actually run the code to increment your counter and update the view, and that throws the "timing" off.
Additionally, many browsers have a "minimum timeout" length, which varies between 4 and about 16 (the latter being the computer's own clock timer), which will really mess with your code.
Instead, you should use delta timing.
var startTime = new Date().getTime();
setInterval(function() {
var elapsed = new Date().getTime()-startTime;
// update view according to elapsed time
},25);
If you're worried about it looking choppy, consider using requestAnimationFrame instead, to update the timer exactly once per frame - this has the added benefit of not updating when the user switches tabs (but it will still be timing them) because if the tab is not active then there's no need to redraw stuff.
You can use the new performance object to get a more accurate time. Combine this with requestAnimationFrame instead of setInterval:
var startTime = performance.now(),
currentTime,
isRunning = true;
loop();
function loop(timeElapsed) {
currentTime = performance.now();
if (isRunning) requestAnimationFrame(loop);
}
Just subtract startTime from currentTime.
I left timeElapsed which contains time elapsed handed by rAF which you can may use also for something (or just ignore it).
One note though: not all browsers support this yet (and some may use prefix) so for mobile you need to use the standard system time object.

JavaScript: Multi Time Zones Clocks

I want to display 3 clocks from 3 different time zones using JavaScript.
I browsed around the web searching for a simple solution but all I found was long scripts and .js extensions, all those to complete a simple task.
Is there an easy way to do this? do I really have to add an additional JS file to complete this task?
Thanks in advance to the helpers!
Is there an easy way to do this?
Yes.
do I really have to add an additional JS file to complete this task?
No. However, time handling in JS is difficult, since it has no really cross-browser-safe date/timestring parsing and formatting methods. It can be helpful to use a library for that, however that won't be necessary for your clock.
// all three clocks represent current time
var clock1 = new Date(); // current moment
var clock2 = new Date();
var clock3 = new Date();
// for outputting, adjust them
// leave clock1 in UTC
clock2.setHours(clock2.getHours() + 3); // UTC+3
clock3.setHours(clock3.getHours() - 5); // UTC-5
// now for display, use these values:
clock1.getUTCHours();
clock1.getUTCMinutes();
clock1.getUTCSeconds();
clock2.getUTCHours();
clock2.getUTCMinutes();
clock2.getUTCSeconds();
clock3.getUTCHours();
clock3.getUTCMinutes();
clock3.getUTCSeconds();

Settimeout not working when window loses focus

I have a simple JavaScript chronograph that displays on a form field called "d2", it is used to check how long someone takes on doing a specific task:
var milisec=0
var seconds=0
var complemento1=""
document.form1.d2.value='00:00:00'
function display(){
if (milisec>=9){
milisec=0
seconds+=1
}
else{
milisec+=1
}
complemento1=complemento2=complemento3="";
if ((seconds%60)<10) complemento1="0";
if ((Math.floor(seconds/60)%60)<10) complemento2="0";
if ((Math.floor(seconds/3600))<10) complemento3="0";
document.form1.d2.value=complemento3+Math.floor(seconds/3600)+":"+complemento2+(Math.floor(seconds/60)%60)+":"+complemento1+(seconds%60)
setTimeout("display()",100)
}
The problem is that when the person opens a new tab / uses another program the timer stops, and then resumes when the window is focused again (Using Chrome). It has the weirdest behavior, because sometimes it works, sometimes it doesn't.
I saw many posts that needed a script to stop when not on focus, I want the exact opposite and searched for over an hour with no luck. Your help is greatly appreciated!
JavaScript timeouts are not guaranteed be executed at a specific time. For example if the thread is busy with something else at the time when the timer finishes, it will first finish what it is doing and then execute your timer.
Also your function does not take into account the time spend inside the display function, so a little delay will be added for each millisecond.
The correct way to implement a timer is using the system time.
So something like:
//Call at the beggining to save the start time
var start_time = new Date()
// Compute seconds (does not matter when/how often you call it.)
var milliseconds_since_start = new Date().valueOf() - start_time
The Date object can also format this period as a clock for you:
var m = new Date(milliseconds_since_start)
m.getMinutes()+":"+m.getSeconds()

Is it possible to make an alarm in javascript?

Is it possible to ser a function to start in a given date and hour? How?
I thought about setTimeout, but what's the maximum time I can set?
--update
By the way, it's for a desktop application.
I agree with JCOC611 - if you can make sure that your application does not close, then just get a Date object of when your alarm should go off and do something like this:
window.setTimeout(function() { soundAlarm() },
alarmDate.getTime() - new Date().getTime());
I see no reason for this not to work, but a lot of people exalt a timer based solution where you have a short lived timer that ticks until the set time. It has the advantage that the timer function can also update a clock or a countdown. I like to write this pattern like this:
(function(targetDate) {
if (targetDate.getTime() <= new Date().getTime()) {
soundAlarm();
return;
}
// maybe update a time display here?
window.setTimeout(arguments.callee,1000,targetDate); // tick every second
})(alarmDate);
This is basically a function that when called with a target date to sound an alarm on, re-calls itself every second to check if the time has not elapsed yet.
setTimeout(functionToCall,delayToWait)
As stated in Why does setTimeout() "break" for large millisecond delay values?, it uses a 32 bit int to store the delay so the max value allowed would be 2147483647
Does setTimeout() have a maximum?
http://www.highdots.com/forums/javascript/settimeout-ecma-166425.html
It may surprise you that setTimeout is
not covered by an ECMA standard, nor
by a W3C standard. There are some
holes in the web standards. This is
one of them. I'm looking to the WHAT
Working Group to fix this. See
http://www.whatwg.org/specs/web-apps/current-work/
There doesn't seem to be a problem in
setting the timeout value to something
that is vastly greater than the MTBF
of the browser. All that means is that
the timeout may never fire.
http://javascript.crockford.com/
-Douglas Crockford
As others have mentioned, this isn't the way to handle the situation. Use setTimeout to check a date object and then fire the event at the appropriate time. Some code to play with is linked below.
http://www.w3schools.com/js/tryit.asp?filename=tryjs_timing_clock
You should not relay on setTimeout for the actual alarm trigger but for a periodic function tracking the alarm. Use setTimeout to check the stored time for your alarm say every minute. Store that time in DB, file or server.
Is there any server component to this at all? You could use setInterval to call something serverside on a regular basis via ajax, then pull back a date object and once it's finally in the past you could trigger your "alarm"

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