I have succeeded in cobbling together pieces of code that achieve my goal. However, I would like some advice from more advanced vanilla JS programmers on how I can go about reaching my goal in a better way.
To start, I want to introduce my problem. I have a piece of text on my website where a portion is designed to change every so often. For this, I am running through a loop of phrases. To run this loop continuously, I first call the loop, then I call it again with setInterval timed to start when the initial loop ends. Here is the code I've got, which works even if it isn't what could be considered quality code:
function loop(){
for (let i = 0; i < header_phrases.length; i++){
(function (i) {
setTimeout(function(){
header_txt.textContent = header_phrases[i];
}, 3000 * i);
})(i);
};
}
loop();
setInterval(loop, 21000);
Is there a better way to right this code for both performance and quality? Do I need to use async? If so, any material I can see to learn more? Thanks!
You can implement the same logic using recursion.
function recursify(phrases, index = 0) {
header_txt.textContent = phrases[index];
setTimeout(function () {
recursify(phrases, index < phrases.length - 1 ? index + 1 : 0);
}, 300)
}
recursify(header_phrases);
The function 'recursify' will call itself after 300 miliseconds, but everytime this function gets called, the value of index will be different.
If I understand your requirement correctly, you want top populate an element from an array of values.
A simple way to do this is:
doLoop();
function doLoop() {
var phraseNo=0;
setTimeout(next,21000);
next();
function next() {
header_txt.textContent = header_phrases[phraseNo++];
if(phraseNo>=header_phrases.length) phraseNo=0;
}
}
This simply puts the next() function on the queue and waits.
The call to next() before the function simply starts it off without waiting for the timeout.
this is assuming that header_txt and header_phrases are not global vars. using global vars isn't a good idea.
var repeatIn = 3000;
phraseUpdater();
function phraseUpdater() {
var updateCount = 0,
phrasesCount = header_phrases.length;
setHeader();
setTimeout(setHeader, repeatIn);
function setHeader() {
header_txt.textContent = header_phrases[updateCount++ % phrasesCount] || '';
}
}
guys. It's a timer. I wanna run the timer and when it's end do something else(like a warning),and then run again with other amount of minutes. But I can't cause always only the second call is executed:
$(document).ready(function() {
timer(5,timer(25));
// timer(5);
// timer(25); do not work... only exec de last one
});
function timer(countTo,callback){
var time = 10; /* how long the timer runs for */
var initialOffset = '440';
var i = 1
var interval = setInterval(function() {
$('.circle_animation').css('stroke-dashoffset', initialOffset-(i*(initialOffset/countTo)));
$('h2').text(i);
if (i == countTo) {
clearInterval(interval);
}
i++;
}, 1000);
callback();
}
Which is the best solution? There is something that I am not understanding... Thanks anyway!
Well, first off:
timer(5,timer(25));
If you think this line will execute timer(5), and then at the end of timer(5) it will execute timer(25), you are mistaken. This is actually going to evaluate timer(25) immediately, and pass its return value (undefined) as the second parameter to timer(5,undefined).
If you intended to pass that as a callback, you need to pass a function. So you could do:
timer(5,timer.bind(null,25));
But, for that matter, you don't even check if callback exists before attempting to invoke it, so you probably are getting a reference error anyway.
timer(5,timer(25));
starts two timers and passes the result of the second (undefined) to the first as callback. You want:
timer(5,timer.bind(window,25));
And the callback needs to be executed if i==countTo ...
Is this what you want?
timer(5,function(){timer(25)});
Your problem is here:
timer(5,timer(25));
You should type
timer(5, function(){
timer(25)
});
//or using ES6 syntax
timer(5, () => timer(25));
because timer(25) returns its value (this function doesn't return value so it tries to invoke undefined), not that function.
Also read about closures, it might be helpful.
Instead of runing a callback(), you need to run the function itself (timer()). You'll also need to run a for loop inside your function that checks how many times the function has already run. If it reaches your desired maximum, break out of that. This way it won't run indefinitely.
In the following example, the timer() function executes five times, which is what I'm assuming you want by calling timer(5).
$(document).ready(function() {
timer(5);
});
function timer(countTo) {
for (var iterations = 0; iterations < countTo; iterations++) {
var time = 10; /* how long the timer runs for */
var initialOffset = '440';
var i = 1
var interval = setInterval(function() {
$('.circle_animation').css('stroke-dashoffset', initialOffset - (i * (initialOffset / countTo)));
$('h2').text(i);
if (i == countTo) {
clearInterval(interval);
}
}, 1000);
timer();
console.log("Iteration:", iterations + 1);
}
}
<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
To run the function 25 times after this, all you have to do is call timer(25) directly after timer(5):
$(document).ready(function() {
timer(5);
timer(25);
});
$(document).ready(function() {
timer(5);
timer(25);
});
function timer(countTo) {
for (var iterations = 0; iterations < countTo; iterations++) {
var time = 10; /* how long the timer runs for */
var initialOffset = '440';
var i = 1
var interval = setInterval(function() {
$('.circle_animation').css('stroke-dashoffset', initialOffset - (i * (initialOffset / countTo)));
$('h2').text(i);
if (i == countTo) {
clearInterval(interval);
}
}, 1000);
timer();
console.log("Iteration:", iterations + 1);
}
}
<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
Hope this helps! :)
I am trying to loop through an array, but want to output each value of the array with a delay. This is what my current understanding is on how it should work:
EDIT
Requested JS Fiddle: http://jsfiddle.net/d3whkjww/
loopThroughSplittedText: function(splittedText) {
for (var i = 0; i < splittedText.length; i++) {
// for each iteration console.log a word
// and make a pause after it
setTimeout(
console.log(splittedText[i]),
1000
);
};
},
Yet, it does not work, and I believe it might be, because the arguments in the "for" loop have to be inside the setTimeout function. Yet I don't know how to make it work.
All I get is every value of the array at once, but I want them appear with a delay. How do I do that?
var splittedText = ["Hello", "World", "How", "Are", "You", "Today"];
function loopThroughSplittedText(splittedText) {
for (var i = 0; i < splittedText.length; i++) {
// for each iteration console.log a word
// and make a pause after it
(function (i) {
setTimeout(function () {
document.getElementById('text').innerHTML += splittedText[i];
console.log(splittedText[i]);
}, 1000 * i);
})(i);
};
}
loopThroughSplittedText(splittedText);
Fiddle Demo
Chances are you're going to want to use a recursive function instead of a for loop here. However, I'll explain both ways just in case you (or someone else reading this) has your heart set on doing this with a loop.
For a recursive function, the general idea is that you'll want to call the function once, then let it call itself repeatedly until it's finished doing what you want it to do. In terms of code, it will could look something a bit like this:
loopThroughSplittedText: function(splittedText) {
// Create our counter; delayedOutput will use this to
// track how far along in our string we are currently at
var locationInString = 0;
function delayedOutput() {
// Output the next letter in our string
console.log(splittedText[locationInString]);
// Increment our counter so that on the next call we are on the next letter
locationInString++;
// Only perform setTimeout if we still have text left to output
if (locationInString < splittedText.length) {
// Functions can reference themselves using their own name
setTimeout(delayedOutput, 1000);
}
}
// Call our function once to get things started
delayedOutput();
},
Alternatively, if you really prefer using a loop, you can still do it, but there's a fair bit of fiddling that has to be done to accomplish this.
First, you're going to need to place console.log within its own function. This is because when you place console.log(something), you're not actually passing it, but calling it right then and there, which is not what you want; by calling it, it spits out the text to the console right away rather than waiting until later. Tucking it away in its own function allows it to be passed to setTimeout so it can be called later on.
Second, you're going to have to wrap that function in yet another function to ensure that it's given the correct value of i when it fires. The reason is effectively this: Your intention is to tell the function "when you're ready, use what i was when I set you up." However, what you're doing right now is effectively saying "when you're ready, look at i". Because the function doesn't check what i is until it's ready to fire, it won't know its value until long after you have performed the loop, meaning i will be a number much higher than you want!
As a bit of a sub-point to the above, you'll want to call that function immediately. This is known as an immediately invoked function expression. If you're not familiar with them, they're certainly worth looking up. Their uses are a bit unusual, but they're a powerful tool in the right spot.
Finally, because you're setting up everything right here and now, you want to make sure the timeout for each function is a second apart; as it stands now, you're saying "do all of these one second from now", when your intention is "do all of these one second apart, starting one second from now". This fix is relatively easy; all you need to do is multiply your timeout by i so that you set up the first to go 1 second from now, the second to go 2 seconds from now, and so on.
All of that combined gives you code that looks something like this:
loopThroughSplittedText: function(splittedText) {
for (var i = 0; i < splittedText.length; i++) {
setTimeout(
(function(locationInString) {
return function() {
console.log(splittedText[locationInString]);
};
}(i)),
(1000*i)
);
}
},
As for which solution is better, I would probably recommend the recursive function. The recursive version will only create one function that calls itself for every string you pass it, whereas the for loop version will create one function for every character in the string, which could get out of hand very quickly. Function creation (and object creation in general) can get expensive in JavaScript when you're working on larger projects, so it's generally best to favor solutions that avoid creating massive amounts of functions when possible.
But still, for sake of explanation, I wouldn't want to leave you without the for loop version; the knowledge could come in handy in other places. :)
A recursive function call would do the job:
var a = [
1,2,3,4,5,6,7,8,9,10
];
function log(i){
console.log(a[i]);
if (i<a.length){
setTimeout(function(){
i++;
log(i);
},1000);
}
}
log(0);
http://jsfiddle.net/Curt/rjve4whe/1/
In my example, it will show you how to loop through an array contentiously until you stop. This is to just give you an idea on how you can do the delay. Also it shows you when the value actually got displayed.
I would say that you could actually create a nice utility from this timer, and use it for multiple purposes and with the utility it'll stop you from repeating large chunks of code.
JavaScript Loop example:
var body = document.body;
var splittedText = ["Hello", "World", "How", "Are", "You", "Today"];
loopThroughArray(splittedText, function (arrayElement, loopTime) {
body.innerHTML += arrayElement+ ": " + loopTime+ "<br/>";
}, 1000);
function loopThroughArray(array, callback, interval) {
var newLoopTimer = new LoopTimer(function (time) {
var element = array.shift();
callback(element, time - start);
array.push(element);
}, interval);
var start = newLoopTimer.start();
};
// Timer
function LoopTimer(render, interval) {
var timeout;
var lastTime;
this.start = startLoop;
this.stop = stopLoop;
// Start Loop
function startLoop() {
timeout = setTimeout(createLoop, 0);
lastTime = Date.now();
return lastTime;
}
// Stop Loop
function stopLoop() {
clearTimeout(timeout);
return lastTime;
}
// The actual loop
function createLoop() {
var thisTime = Date.now();
var loopTime = thisTime - lastTime;
var delay = Math.max(interval - loopTime, 0);
timeout = setTimeout(createLoop, delay);
lastTime = thisTime + delay;
render(thisTime);
}
}
Ok, as It is not an exact duplicate, you need to increate the delay in the loop, also escape from the closure variable in a loop issue
loopThroughSplittedText: function (splittedText) {
splittedText.forEach(function (text, i) {
setTimeout(function () {
console.log(text);
}, i * 1000)
})
}
var obj = {
loopThroughSplittedText: function(splittedText) {
splittedText.forEach(function(text, i) {
setTimeout(function() {
document.getElementById('x').innerHTML += text
}, i * 1000)
})
}
}
obj.loopThroughSplittedText('abcde'.split(''))
<div id="x"></div>
One problem with your code is that i is common to all the callbacks. So the first callback is told "output the entry at index i", however by the time it gets to execute the initial loop is finished so i is now at the end of the text.
One way to achieve what you're looking for is to not use a for loop, but to have a function which (1) prints a character, (2) updates the counter/position, and (3) schedules the next character if needed:
loopThroughSplitText: function (text) {
var i = 0;
function printEntry() {
console.log(text[i]);
i++; // Increment the position
if (i < text.length) { // If there are more chars, schedule another
setTimeout(printEntry, 1000);
}
}
printEntry(); // Print the first entry/char
}
solution using closure
https://jsfiddle.net/x3azn/pan2oc9y/4/
function loopThroughSplittedText(splittedText) {
var splittedText = ["Hello", "World", "How", "Are", "You", "Today"];
for (var i = 0; i < splittedText.length; i++) {
// for each iteration console.log a word
// and make a pause after it
(function(_i) {
setTimeout(function() {
window.document.getElementById('text').innerHTML = splittedText[_i];
console.log(splittedText[_i]);
}, 1000)
}(i));
}
}
loopThroughSplittedText()
One more solution, with a setInterval:
var i = 0;
var intv = setInterval(function() {
if (i >= splittedText.length) {
clearInterval(intv);
} else {
console.log(splittedText[i]);
++i;
}
}, 1000);
There are a couple of problems here
setTimeout should take a function, not the result of calling a function
setTimeout returns immediately, so all the actions in your loop will be started at roughly the same moment, and all wait 1000ms before execting (notwithstanding the comment above however, which means they're all executed at the same moment).
The value of i will all be equal to splittedText.length for each iteration due to not wrapping your loop control variable in a closure.
What you need to do, is wait until the setTimeout instructions are executed before moving on to the next iteration of the loop.
For example:
var splittedText = ["Hello", "World", "How", "Are", "You", "Today"];
function loopThroughSplittedText(splittedText) {
displayValue(splittedText,0);
}
function displayValue(arr, i){
if(i<arr.length){
setTimeout(function(){
document.getElementById('text').innerHTML = arr[i];
console.log(arr[i])
displayValue(arr,i+1);
},1000)
}
}
loopThroughSplittedText(splittedText)
Live example: http://jsfiddle.net/d3whkjww/1/
This will also work
function loopThroughSplittedText(splittedText) {
for (var i=0; i < splittedText.length;i++) {
(function(ind, text) {
setTimeout(function(){console.log(text);}, 1000 + (1000 * ind));
})(i, splittedText[i]);
}
}
Another sample:
var split = 'Lorem ipsum dolor'.split(' ');
var loop = function() {
console.log(split[0]);
split = split.slice(1);
if (split.length > 0) {
setTimeout(function() {
loop();
}, 1000);
}
}
loop();
Bringing out an alternative solution to the problem, which is making use of the third argument to setTimeout which is only supported in newer browsers:
(function (splittedText) {
for (var i = 0; i < splittedText.length; i++) {
setTimeout(
function(val) { console.log(val); },
i * 1000,
splittedText[i]
);
}
})(["Hello", "world", "!"]);
API documentation can be seen here (note the optional params).
You can achieve by 3 ways
1. closure
2. Recursive
3. variable declaration using let
var data = ['a', 'b', 'c', 'd'];
closure:
for(i=0; i<=data.length; i++) {
(function(x) {
setTimeout(() => {
console.log(x);
}, 1000)
})(data[i]);
}
let variable declaration
for(const ind of data) {
let local = ind;
setTimeout(() => {
console.log(local);
}, 1000)
}
I'm trying to create fade in and fade out function with JavaScript, but it's not working. Please tell me what I'm doing wrong.I'm not getting transitioning effect.
var fade_in_btn = document.getElementById('fade-in'),
fade_out_btn = document.getElementById('fade-out'),
fading_div = document.getElementById('fading-div');
function sleep(milliseconds) {
var start = new Date().getTime();
for (var i = 0; i < 1e7; i++) {
if ((new Date().getTime() - start) > milliseconds){
break;
}
}
}
fade_out_btn.onclick = function(){
for (var i=100; i >= 0; i--) {
sleep(0010);
opacity_function(i);
}
}
fade_in_btn.onclick = function(){
for (var i=1; i <= 100; i++) {
sleep(0010);
opacity_function(i);
}
}
function opacity_function(opacity_value){
fading_div.style.opacity = opacity_value / 100;
fading_div.style.filter = 'alpha(opacity=' + opacity_value + ')';
console.log(fading_div.style.opacity);
}
Fiddle with HTML.
All code Working Fine. But from my point of view problem is the for...loop is not updating the value of opacity after each iteration; it's only updating the final value.
Please Help me to resolve this problem.
this is a pure JS answer that doesn't use requestAnimationFrame but i have chosen to discard your sleep function since it is an odd choice and bad practice (and yours doesn't work. also note that there can be no true sleep in JS.)
this works:
fade_out_btn.onclick = function(){
var i = 100;
var myint = setInterval(function(){
opacity_function(i);
i--;
if (i<0) clearInterval(myint);
console.log(i);
},10); //this is the number of ms between iterations of the codeblock in my setInterval function
}
[EDIT: some people were recommending setTimeout. I see no need for that, but in case you really want to use setTimeout, this is how I would do it:
var i = 100;
function fadeout(){
var myint = setTimeout(function(){
opacity_function(i);
i--;
if (i>0) fadeout();
},10);
}
fade_out_btn.onclick = fadeout;
notice two things:
1 - I pulled the definition of i outside of the function. you would have to be grabbing that value that you want to decrement from outside the function anyways, because your starting value for a fadeout would presumably not always be 100 but would be set to the current value of the opacity, i.e. the value of fading_div.style.opacity * 100.
2 - i bound a callback to the onclick.
regarding choosing between setInterval and setTimeout:
setInterval and setTimeout both simply schedule the execution of code. setInterval schedules events every x ms from when it is executed whereas a series of chained setTimeouts schedules an event in x ms, then executes again, then schedules another event in x ms. so there is a little bit of time overhead for setTimeout because the real time interval is x + (the time is takes to execute the codeblock once). it is possible have issues with using setInterval if the time it takes to execute once is larger than the specified interval but that would not affect such a simple program as yours. see here]
Sorry if this question has already been asked here before, I could not find a suitable answer.
I am wanting to create a JavaScript sleep/delay/wait function that I can call anywhere in the script, like jQuery's .delay()
I am not able to use setTimeout, as I have a script that is generated by php, and so am not able to put it into two different functions, with the timeout in the middle. I need to create a function that allows me to do
alert("time started");
sleep(4000);
alert("time up");
I really do not want to use jQuery.
Here's a solution using the new async/await syntax.
async function testWait() {
alert('going to wait for 5 second');
await wait(5000);
alert('finally wait is over');
}
function wait(time) {
return new Promise(resolve => {
setTimeout(resolve, time);
});
}
Note: You can call function wait only in async functions
You cannot just put in a function to pause Javascript unfortunately.
You have to use setTimeout()
Example:
function startTimer () {
timer.start();
setTimeout(stopTimer,5000);
}
function stopTimer () {
timer.stop();
}
EDIT:
For your user generated countdown, it is just as simple.
HTML:
<input type="number" id="delay" min="1" max="5">
JS:
var delayInSeconds = parseInt(delay.value);
var delayInMilliseconds = delayInSeconds*1000;
function startTimer () {
timer.start();
setTimeout(stopTimer,delayInMilliseconds);
}
function stopTimer () {
timer.stop;
}
Now you simply need to add a trigger for startTimer(), such as onchange.
You will have to use a setTimeout so I see your issue as
I have a script that is generated by PHP, and so am not able to put it into two different functions
What prevents you from generating two functions in your script?
function fizz() {
var a;
a = 'buzz';
// sleep x desired
a = 'complete';
}
Could be rewritten as
function foo() {
var a; // variable raised so shared across functions below
function bar() { // consider this to be start of fizz
a = 'buzz';
setTimeout(baz, x); // start wait
} // code split here for timeout break
function baz() { // after wait
a = 'complete';
} // end of fizz
bar(); // start it
}
You'll notice that a inside baz starts as buzz when it is invoked and at the end of invocation, a inside foo will be "complete".
Basically, wrap everything in a function, move all variables up into that wrapping function such that the contained functions inherit them. Then, every time you encounter wait NUMBER seconds you echo a setTimeout, end the function and start a new function to pick up where you left off.
The behavior exact to the one specified by you is impossible in JS as implemented in current browsers. Sorry.
Well, you could in theory make a function with a loop where loop's end condition would be based on time, but this would hog your CPU, make browser unresponsive and would be extremely poor design. I refuse to even write an example for this ;)
Update: My answer got -1'd (unfairly), but I guess I could mention that in ES6 (which is not implemented in browsers yet, nor is it enabled in Node.js by default), it will be possible to write a asynchronous code in a synchronous fashion. You would need promises and generators for that.
You can use it today, for instance in Node.js with harmony flags, using Q.spawn(), see this blog post for example (last example there).
You can use this -
function sleep(milliseconds) {
var start = new Date().getTime();
for (var i = 0; i < 1e7; i++) {
if ((new Date().getTime() - start) > milliseconds){
break;
}
}
}
You could use the following code, it does a recursive call into the function in order to properly wait for the desired time.
function exportar(page,miliseconds,totalpages)
{
if (page <= totalpages)
{
nextpage = page + 1;
console.log('fnExcelReport('+ page +'); nextpage = '+ nextpage + '; miliseconds = '+ miliseconds + '; totalpages = '+ totalpages );
fnExcelReport(page);
setTimeout(function(){
exportar(nextpage,miliseconds,totalpages);
},miliseconds);
};
}