Someone know if after I displays an HTML page I can access a specific ID (getElementById), and change it a value several times?
I want to present a client-side some string and change it several times according the progress of the program, but I can not, it writes to me only recently.
For example:
<script type="text/javascript">
function foo(){
for(var i = 0; i<10000; i++){
document.getElementById('myTag').innerHTML = i;
}
}
</script>
In this case, I do not see the numbers run. I see only the last one.
If I put alert inside the loop - the value is changed.
As i understand your question you want a countup from 0 to 10000 ?
and you want to see the progression on screen ? you could do something like that :
http://jsfiddle.net/camus/ayJFM/
var interval = 500;//milliseconds
var foo = (function () {
var i = 0;
var func = function () {
if (i < 10000) {
document.getElementById("myTag").innerHTML = i;
i += 1;
setTimeout(func, interval);
}
};
return func;
})();
setTimeout(foo, interval);
You're almost there. The only thing you're doing wrong is replacing the innerHTML content instead of adding to it. Change this:
document.getElementById('myTag').innerHTML = i;
to this:
document.getElementById('myTag').innerHTML += i;
Additional/alternative answer:
Wait. I've just reread your question and realized that there is another way of interpreting it. The way you ask it is quite vague so I'm leaving the above answer as is.
The reason you don't see "running numbers" as you process the for loop is because you misunderstand how javascript works in the browser.
The browser's event loop runs something like this:
1. Fetch content
2. Run javscript
3. Render content
then repeat forever
This is how javascript works. So running a simple for loop like you're doing. The browser executes the script until there is nothing else to execute (step 2). Once javascript have finished executing then it will start the render process (step 3). Obviously, by this time the value of i is the final value and therefore you only see the final value.
The browser never interrupts running javascript to render/update the page. So, how do people implement countdown timers etc? They do it by scheduling a piece of javascript to execute in the next iteration of the event loop. That is to say, the let the browser enter step 3 and at the appropriate moment as the browser enters step 2 again they run the script they want.
Javascript basically provides two ways to do this: setTimeout and setInterval.
How setTimeout works is this:
step 1. nothing to do
step 2. setTimeout schedules a piece of javascript to run at a later time
Note that the javascript does not execute yet until setTimeout
expires.
step 3. let the browser update the page
many, many loops of steps 1-3
step 2 (some time later).
setTimeout expires and the piece of javascript executes
step 3. let the browser update the page
So, the get the effect you want, you need to do it like this:
function foo(){
var i = 0;
var update = function(){
document.getElementById('myTag').innerHTML = i;
i++;
if (i<10000) {
setTimeout(update,100);
}
};
update();
}
Related
I've encountered a very badly designed website, and most of the "dynamic" content on the site is changed within setTimeout/setInterval functions.
There is one very annoying setInterval function which checks page activity very quickly, and I would like to override this function.
What I tried is clearing all the setInterval values, one by one to check if the function stopped. Also, clearing all the possible setInterval values like this: for(let i = 0; i < 1000; i++) clearInterval(i);, stops the "dynamic" page rendering, WHICH I DONT WANT TO
Question: 1. is there any way to look into the interval or timeout function and clear them?
2. is there a better way?
My current solution: I'm overriding the setInterval and setTimeout before page loaded, and log the function .toString() within.
The short answer is no, you cannot determine anything about the setTimeout/setInterval callback given a timerId. It sounds as if you don't have access to edit the underlying Javascript to prevent this action. If you can get your JS to load before the code in the page, then what you can do is replace setInterval or setTimeout with your own code, where you can increase the interval to whatever you want. For example:
let setTimeoutOld = setTimeout;
setTimeout = (cb, interval) => {
if (interval < 1000) {
interval = 1000;
}
setTimeoutOld(cb, interval);
}
Now if the page does something like:
setTimeout(() => { console.log('fired') }, 1);
The timeout won't fire until at least 1000ms have passed. If you only wanted to modify a specific setTimeout based on the contents of the cb, you could do what you mentioned in your work-around: calling .toString() on the function and comparing it to some previously generated .toString() (partial or complete) and then doing whatever you wanted.
I assume you have access to code wherever it's setting timeout or interval.
So just take a global array and push it's output to it. Then iterate that array to clear everything.
For ex.
timeouts = [];
now, in code where there's timeout like
var timeout = setTimeout(<callback> , <interval> ); // push it's output to that global.
timeouts.push(timeout);
Then at the very end clear that.
for(time of timeouts) {
clearTimeout(time);
}
Similarly, for Interval.
Hope this is what you are looking for.
I have an array of URL's and I want to go to every page to parse some information. I do:
var numbers = ["1111", "2222", "3333"];
function parse(page){...
}
function set(page){
console.log(page);
window.location = page;
parse (page);
}
for (j=0,m = numbers.length; j<m; j++){
page="http://www.*****/*****/"+numbers[j]+"/*****/";
setInterval(set(page), 10000);
}
But it's not working because browser tries to download pages and at the end, only the last one will be displayed. Function "parse" does not parse pages. How to fix my code?
setInterval will call your set function once every 10 seconds the way you have invoked it. The for loop will have ended before that time, and the page's value at that time will be:
"http://www.*****/*****/3333/*****/";
So after 10 seconds you will only see that page displayed.
Try use setTimeout combine with recursive call.
const MAX=100;
setPage(num){
parse()
if(num<MAX)
setTimeout(setPage(num+1), 10000);
}
When you use setInterval(), you just tells the browser to carry out set() function after 10 seconds, and because all the setInterval() are been called in a very short period of time in that for loop, they will carry out the task together as well, then set will be carried out thrice, first with "1111" then "2222" and "3333".
It would seems like it only run the last one with "3333".
I suggest you use setInterval() only once, while the page variable will be created with a counter.
var counter=0
function count(){
page="http://www.*****/*****/"+numbers[counter]+"/*****/";
set(page);
counter+=1;
if(counter>=numbers.length){
counter=0;
}
}
setInterval(count(), 10000);
It is due to Scopes and Closures in JS. The solution for the problem is to create IIFE(Immediately Invoked Function Expression) inside loop!
for (var i=1; i<=5; i++) {
page="http://www.*****/*****/"+numbers[j]+"/*****/";
(function(j){
setTimeout( set(page), 10000 );
})( i );
}
If you have time, refer about Closures in JS!
I am trying to make a series of synchronous calls into asynchronous, and I'm using when...done... I'm new at this stuff, but from all the reading I've been doing on this subject the last two days, my code below should work. Well, it does work, but not exactly in the way that I meant for it.
In my test code below I make five calls, and each one would take a different amount of time (in my example, it's based on the length of the string... 1/2 a second per character). My expectation was that the calls that took less time (i.e. the shorter length strings in my example) would complete first I fire off all five calls quickly, and would expect the results to be displayed in order of shorter execution to longer execution.
Here's my code:
var cars = ["Saab", "Chrysler", "Volvo", "BMW", "GT"];
loopAll(cars);
document.getElementById("demo").innerHTML += "Start!<br>";
function loopAll(array) {
for (var i in array) {
$.when( encapsulate(array[i]) ).done( printIt );
}
function encapsulate(name){
var a = $.Deferred();
setTimeout(function(){pause(name.length*500);a.resolve(name);}, 0);
return a;
}
}
function printIt(name){
document.getElementById("demo").innerHTML += name + "<br>";
}
function pause(ms) {
ms += new Date().getTime();
while (new Date() < ms){}
}
Each of the elements in the array get printed, and I can see them popping on the display one by one. However, they seem to be synchronous in that they are being displayed in the original order of the array, and the pause is occurring between each of the displayed elements. However, my expectation was that the shorter executing functions finishing (and displaying) sooner than the longer ones.
Note: I am NOT trying to sort the array. My intent is to fire off multiple calls and let the shorter executing ones finish first, and not sequentially. I'm using the array of strings only as an example.
The timeout block isn't really doing anything in this scenario. It will immediately execute its function block.
JavaScript is single threaded, by using that homebrewed 'pause' method you are effectively blocking the thread and causing each loop to be executed synchronously.
If you have some synchronous code, and an asynchronous alternative isn't available, you may be able to use web workers to shift them off of the main thread.
http://www.html5rocks.com/en/tutorials/workers/basics/
In my test code below I make five calls, and each one would take a
different amount of time (in my example, it's based on the length of
the string... 1/2 a second per character).
At
setTimeout(function(){pause(name.length*500);a.resolve(name);}, 0);
the duration appear to be set to 0 for each $.Deferred() object created ? Not certain about expected result of pause ?
My expectation was that the calls that took less time (i.e. the
shorter length strings in my example) would complete first I fire off
all five calls quickly, and would expect the results to be displayed
in order of shorter execution to longer execution.
try setting duration of setTimeout to name.length*500
var cars = ["Saab", "Chrysler", "Volvo", "BMW", "GT"];
loopAll(cars);
document.getElementById("demo").innerHTML += "Start!<br>";
function loopAll(array) {
for (var i in array) {
$.when( encapsulate(array[i]) ).done( printIt );
}
function encapsulate(name){
var a = $.Deferred();
setTimeout(function(){a.resolve(name);}, name.length*500);
return a;
}
}
function printIt(name){
document.getElementById("demo").innerHTML += name + "<br>";
}
// function pause(ms) {
// ms += new Date().getTime();
// while (new Date() < ms){}
// }
<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.11.1/jquery.min.js"></script>
<div id="demo"></div>
The code you listed is a bit of a red herring; the problem, it turns out, is in the statement "I am trying to make a series of synchronous calls into asynchronous." In most JavaScript environments, this simply isn't possible.
JS environments are generally single threaded, so even if you use setTimeout to schedule code execution for some time in the future, that code will still block the thread. See this JSFiddle for an example: http://jsfiddle.net/BinaryMuse/r4ct92c5/
Unless you use something like Web Workers (in the browser) or external processes, fibers, or native addons in Node, you can't execute JS code asynchronously.
I am using a Javascript function to animate counting a number up. Whenever that function runs Safari doesn't allow any other Javascript to run on the page, including actions associated with the navigation.
Here is the code:
function animateCountUp(containerSpan){
//We pull the max number from the data-number attribute on the container span.
var maxNumber = containerSpan.attr('data-number');
maxNumber = Number(maxNumber);
//Add active class at start and remove at the end. This way we don't run it again while it's already running.
//This was required for IE7 and IE8.
containerSpan.addClass('active');
var currentNumber = 0;
var i = setInterval(function(){
if(currentNumber <= maxNumber){
containerSpan.text(currentNumber);
currentNumber++;
}
else{
clearInterval();
containerSpan.removeClass('active');
}
}, 1);
}
Any feedback would be much appreciated. Thanks.
I see multiple issues:
Is containerSpan a jQuery object?
You are never stopping the interval because you aren't passing the interval ID to clearInterval like clearInterval(i).
Your interval time is set to 1ms. That's basically going to use max CPU and go way faster than can visually be seen.
If containerSpan is a jQuery object, I would try this:
function animateCountUp(containerSpan){
//We pull the max number from the data-number attribute on the container span.
var maxNumber = containerSpan.data('number');
//Add active class at start and remove at the end. This way we don't run it again while it's already running.
//This was required for IE7 and IE8.
containerSpan.addClass('active');
var currentNumber = 0;
var timer = setInterval(function(){
if(currentNumber <= maxNumber){
containerSpan.text(currentNumber);
currentNumber++;
} else {
clearInterval(timer);
containerSpan.removeClass('active');
}
}, 50);
}
Beyond this, you need to check your error console or debug console to see what javascript errors are being reported. That should always be the very first thing you look at when scripts aren't running as expected.
is containerSpan a jquery object( i.e. $('nameOf the object')) because it looks like you're using jquery methods but i dont see any jquery objects for them to be used on
try right clicking and using inspect element to see if there are any errors in your console log
I am using Selenium to test a web app that uses Dojo, and it uses java script to display certain elements. I want to wait until all of the elements are desplayed before I try to manipulate the page, however I am having trouble.
I have started by waiting for the dojo inFlight variable to be 0, this says that all ajax has finished. This doesn't always work because it seems to do some things on a timeout afterwards.
I have also tried repeatedly looking for the element, but this isn't too nice, as perhaps there is some javascript later which will use this field in some way.
So basically I want a method (in firefox at least) to query the javascript waiting to run on a setTimeout (or setInterval) I could even cope with a way of wrapping the built in call through a function of my own just to keep track of this.
Any thoughts or suggestions appreciated!
Every function in JavaScript can be replaced. Consider something like this:
window.originalSetTimeout = window.setTimeout;
window.setTimeout = function(func, delay, params) {
window.timeoutCounter++;
window.originalSetTimeout(window.timeoutCallback, delay, [func, params]);
}
window.timeoutCallback = function(funcAndParams) {
window.timeoutCounter--;
func = funcAndParams[0];
params = funcAndParams[1];
func(params);
}
Then:
selenium.waitForCondition("window.timeoutCounter == 0");
Whenever you call setTimeout of setInterval -- a timer id is returned.
Save that timer id in an array
Inside the function that you're calling on the timeout, pop that timer id off the array. Because we have to remove that id from the array as soon as the timer ends.
Any time you want to check the no. of active timers, just query the length of that array.
Another approach could be like this
const timeoutIndexThen = setTimeout(() => {});
// Some code that might call timeouts...
const timeoutIndexNow = setTimeout(() => {});
const countOfTimeoutsFiredSinceThen = timeoutIndexNow - timeoutIndexThen - 1;
It is based on the fact that each timeout will return a number that is greater by 1 on each call.
So we create some dummy timeout just to get this number at some point.
Then, after a while we call it again and we get a new number. Difference between those numbers is how many times interval was called in between.
Downside of this is that you have to actually create the timeout. Upside is that you don't have to modify original function.