I have some data collected in real time that I want to plot to line charts.
I would like to plot the data received in say last 60 calls into a line chart(pause plotting when not pulling data), each name:value pair gets 1 chart(so there would be 6 charts in this case). Of course I need to update the charts every second or every time httpGet() gets called.
I am not sure how to proceed to next step after I have got response(the data to plot) from the server...the end I am looking for is pretty much something "CPU usage history" style.
Here is my JavaScript file for collecting data from an aggregation server:
//httpGet() adopted from SO/247483
function httpGet()
{
var xmlHttp = new XMLHttpRequest();
xmlHttp.open( "GET", "foo.com/sensordata", false );
xmlHttp.send( null );
console.log(xmlHttp.responseText);
return xmlHttp.responseText;
}
var interval;
//this is called by a button in the html file
function start(btn)
{
if(btn.value=="Start"){
interval = setInterval(httpGet, 1000);
btn.value="Stop";
} else {
btn.value="Start";
clearInterval(interval);
}
}
So clicking the "Start" button will start making GET requests for data every 1 second. Server returns data in JSON format, this is an example output from console:
{
"Time":"2015/06/04 18:35:39",
"SensorA":{"Value1":0.34804,"Value2":-0.39175,"Value3":-0.61718},
"SensorB":{"Value1":516,"Value2":1,"Value2":2103}
}
Thank you!
I've made this demo (be sure to click on the Start Feed button!) that uses ZingChart. In the callback for the get request, I loop through the data and put it into the right format for ZingChart, then when it's all scrubbed, I use the modify method to set the values attribute in scale-x, which takes an array of Unix time values in milliseconds, and the setseriesvalues method to update the data in the chart.
for(var i = 0; i < 6; i++){
zingchart.exec('myChart','modify',{
update:false,
data:{
"scale-x":{
"values":dataObj.date
}
}
});
zingchart.exec('myChart','setseriesvalues',{
update:false,
graphid:i,
values:[dataObj[Object.keys(dataObj)[(i + 1)]]]
});
}
zingchart.exec('myChart','update');
Since I'm calling modify and setseriesvalues a bunch of times in a row, I set the update option on both to false, which queues up the changes, with everything that has been queued being pushed to the chart when update is called.
(Yeah, I do fake the data here -- I'm alternating between two different JSON files, but you should get the idea.)
Related
having some issues with the HERE maps api outputting the data i'm requesting too many times. I need it to output only once every 10 seconds, however it is doing it far more times than that.
The code I have here is as follows:
function getMapCorners() {
var mapView = map.getViewModel();
var mapCorners = mapView.b.bounds.cb.X;
var corners = [mapCorners[9], mapCorners[10], mapCorners[3], mapCorners[4]];
console.log(corners);
}
map.addEventListener("mapviewchange", function () {
setTimeout(getMapCorners, 10000);
});
I need to grab these specific co-ordinates as this is feeding into another API that is creating markers on the map in specific areas. When zooming in, it does wait 10 seconds to run the function, but then it throws out the co-ordinate changes for every change in the map's view model during that 10 seconds.
The other API has a request limit of 100 every 15 minutes. So I need this to change so that it will run the function every 10 seconds, and it will only output the information for the final viewModel when the function runs.
If you want to run getMapCorners once every 10 seconds, then do this:
function doEveryTenSeconds(){
getMapCorners();
setTimeout(doEveryTenSeconds, 10000);
}
doEveryTenSeconds();
First, please don't use internal name of objects like .b.bounds.cb.X - b, cb, X are defined by compilation of js library and will be changed for new version of JS API. Please use for it a name of methods and objects described in documentation: https://developer.here.com/documentation/maps/3.1.29.0/api_reference/H.map.ViewModel.html#getLookAtData like:
var mapCorners = map.getViewModel().getLookAtData().bounds.getBoundingBox();
Second, the map event 'mapviewchange' runs multiply times during interacting with map therefore you get multiply times run of function getMapCorners. Suggestion to achieve what you want:
function getMapCorners() {
console.log("getMapCorners!!!", map.getViewModel().getLookAtData().bounds.getBoundingBox());
map.addEventListener("mapviewchange", onMapViewChange);
}
function onMapViewChange() {
map.removeEventListener("mapviewchange", onMapViewChange);
setTimeout(getMapCorners, 10000);
}
See please full code there on https://jsfiddle.net/1m8fvLjy/1/
If I am here asking it is because we are stuck on something that we do not know how to solve. I must admit, we already searched in StackOverflow and search engines about a solution.. but we didn't manage to implement it / solve the problem.
I am trying to create a JavaScript function that:
detects in my html page all the occurrences of an html tag: <alias>
replaces its content with the result of an Ajax call (sending the
content of the tag to the Ajax.php page) + localStorage management
at the end unwraps it from <alias> tag and leaves the content returned from ajax call
the only problem is that in both cases it skips some iterations.
We have made some researches and it seems that the "problem" is that Ajax is asynchronous, so it does not wait for the response before going on with the process. We even saw that "async: false" is not a good solution.
I leave the part of my script that is interested with some brief descriptions
// includes an icon in the page to display the correct change
function multilingual(msg,i) {
// code
}
// function to make an ajax call or a "cache call" if value is in localStorage for a variable
function sendRequest(o) {
console.log(o.variab+': running sendRequest function');
// check if value for that variable is stored and if stored for more than 1 hour
if(window.localStorage && window.localStorage.getItem(o.variab) && window.localStorage.getItem(o.variab+'_exp') > +new Date - 60*60*1000) {
console.log(o.variab+': value from localStorage');
// replace <alias> content with cached value
var cached = window.localStorage.getItem(o.variab);
elements[o.counter].innerHTML = cached;
// including icon for multilingual post
console.log(o.variab+': calling multilingual function');
multilingual(window.localStorage.getItem(o.variab),o.counter);
} else {
console.log(o.variab+': starting ajax call');
// not stored yet or older than a month
console.log('variable='+o.variab+'&api_key='+o.api_key+'&lang='+o.language);
$.ajax({
type: 'POST',
url: my_ajax_url,
data: 'variable='+o.variab+'&api_key='+o.api_key+'&lang='+o.language,
success: function(msg){
// ajax call, storing new value and expiration + replace <alias> inner html with new value
window.localStorage.setItem(o.variab, msg);
var content = window.localStorage.getItem(o.variab);
window.localStorage.setItem(o.variab+'_exp', +new Date);
console.log(o.variab+': replacement from ajax call');
elements[o.counter].innerHTML = content;
// including icon for multilingual post
console.log(o.variab+': calling multilingual function');
multilingual(msg,o.counter);
},
error: function(msg){
console.warn('an error occured during ajax call');
}
});
}
};
// loop for each <alias> element found
//initial settings
var elements = document.body.getElementsByTagName('alias'),
elem_n = elements.length,
counter = 0;
var i = 0;
for(; i < elem_n;i++) {
var flag = 0;
console.info('var i='+i+' - Now working on '+elements[i].innerHTML);
sendRequest({
variab : elements[i].innerHTML,
api_key : settings.api_key,
language : default_lang,
counter : i
});
$(elements[i]).contents().unwrap().parent();
console.log(elements[i].innerHTML+': wrap removed');
}
I hope that some of you may provide me some valid solutions and/or examples, because we are stuck on this problem :(
From our test, when the value is from cache, the 1st/3rd/5th ... values are replaced correctly
when the value is from ajax the 2nd/4th .. values are replaced
Thanks in advance for your help :)
Your elements array is a live NodeList. When you unwrap things in those <alias> tags, the element disappears from the list. So, you're looking at element 0, and you do the ajax call, and then you get rid of the <alias> tag around the contents. At that instant, element[0] becomes what used to be element[1]. However, your loop increments i, so you skip the new element[0].
There's no reason to use .getElementsByTagName() anyway; you're using jQuery, so use it consistently:
var elements = $("alias");
That'll give you a jQuery object that will (mostly) work like an array, so the rest of your code won't have to change much, if at all.
To solve issues like this in the past, I've done something like the code below, you actually send the target along with the function running the AJAX call, and don't use any global variables because those may change as the for loop runs. Try passing in everything you'll use in the parameters of the function, including the target like I've done:
function loadContent(target, info) {
//ajax call
//on success replace target with new data;
}
$('alias').each(function(){
loadContent($(this), info)
});
I have a JSON data of news like this:
{
"news": [
{"title": "some title #1","text": "text","date": "27.12.15 23:45"},
{"title": "some title #2","text": "text","date": "26.12.15 22:35"},
...
]
}
I need to get a certain number of this list, depended on an argument in a function. As I understand, its called pagination.
I can get the ajax response and slice it immediately. So that every time the function is called - every time it makes an ajax request.
Like this:
function showNews(page) {
var newsPerPage = 5,
firstArticle = newsPerPage*(page-1);
xhr.onreadystatechange = function() {
if(xhr.readyState == 4) {
var newsArr = JSON.parse(xhr.responseText),
;
newsArr.news = newsArr.news.slice(firstArticle, newsPerPage*(page));
addNews(newsArr);
}
};
xhr.open("GET", url, true);
xhr.send();
Or I can store all the result in newsArr and slice it in that additional function addNews, sorted by pages.
function addNews(newsArr, newsPerPage) {
var pages = Math.ceil(amount/newsPerPages), // counts number of pages
pagesData = {};
for(var i=0; i<=pages; i++) {
var min = i*newsPerPages, //min index of current page in loop
max = (i+1)*newsPerPages; // max index of current page in loop
newsArr.news.forEach(createPageData);
}
function createPageData(item, j) {
if(j+1 <= max && j >= min) {
if(!pagesData["page"+(i+1)]) {
pagesData["page"+(i+1)] = {news: []};
}
pagesData["page"+(i+1)].news.push(item);
}
}
So, simple question is which variant is more effective? The first one loads a server and the second loads users' memory. What would you choose in my situation? :)
Thanks for the answers. I understood what I wanted. But there is so much good answers that I can't choose the best
It is actually a primarily opinion-based question.
For me, pagination approach looks better because it will not produce "lag" before displaying the news. From user's POV the page will load faster.
As for me, I would do pagination + preload of the next page. I.e., always store the contents of the next page, so that you can show it without a delay. When a user moves to the last page - load another one.
Loading all the news is definitely a bad idea. If you have 1000 news records, then every user will have to load all of them...even if he isn't going to read a single one.
In my opinion, less requests == better rule doesn't apply here. It is not guaranteed that a user will read all the news. If StackOverflow loaded all the questions it has every time you open the main page, then both StackOverflow and users would have huge problems.
If the max number of records that your service returns is around 1000, then I don't think it is going to create a huge payload or memory issues (by looking at the nature of your data), so I think option-2 is better because
number of service calls will be less
since user will not see any lag while paginating, his experience of using the site will be better.
As a rule of thumb:
less requests == better
but that's not always possible. You may run out of memory/network if the data you store is huge, i.e. you may need pagination on the server side. Actually server side pagination should be the default approach and then you think about improvements (e.g. local caching) if you really need them.
So what you should do is try all scenarios and see how well they behave in your concrete situation.
I prefer fetch all data but showing on some certain condition like click on next button data is already there just do hide and show on condition using jquery.
Every time call ajax is bad idea.
but you also need to call ajax for new data if data is changed after some periodic time
I would like to do a progress bar for the time when the database synchronize. The request which counts the number of documents to synchronize is too long. I tried with the request GET _active_tasks on the couchdb database but it returns an empty json. I tried with the change event of the Pouchdb function replicate but the info variable doesn't display. Have you others technics for the progress bar or would you know how used the technics I have ever tried ?
I have not found a perfect solution, but one that seemed 'good enough' for us has been
get info about source db, to know what the 'end goal' is.
Add a 'changes' callback (like you mentioned in your answer), where you receive an info object with the last_seq that has been replicated. Divide this with the update_seq you got from the source, and update your progress bar.
~
Q.all(source.info())
.then(function(sourceInfo) {
var replication = source.replicate.to(target);
var startingpoint;
replication.on('change', function(info) {
// the first time we get a replication change,
// take the last_seq as starting point for the replication
// and calc fractions based on that
var fraction = 0;
if(typeof startingpoint === "undefined") {
startingpoint = info.last_seq;
} else {
fraction = (info.last_seq - startingpoint) / (sourceInfo.update_seq - startingpoint);
}
// Whatever you need to do to update ui here
updateUi(fraction);
});
})
This might be a newb question but....
Recently, I have been using window.setTimeout which makes a recursive call to the parent function, which makes an ajax poll to the server.
function connectToVM(portal) {
//making the ajax call here....
if(response.responseText !== "")
{
windowInterval = window.setTimeout(function() {
connectToVM(portal)
}
, 4000);
}
}
windowInterval is my global var here.
if(!checkIfChartExists()) {
window.clearInterval(windowInterval);
}
Now, instead of making use of variables here, I know that I can simple pass the function to clearTimeout, but that also causes all the other intervals to be stopped :(
The reason why I am doing this is the server does a timeout, only when there is a response.
My scenario is, I have a chart which updates every timeout interval.
AFAIK, when we set the interval, there is a specific value set to the variable(if set to a variable). So when I print my variable(every time when the timeout function is called), I get some int values which are unique.
I have many tabs, and many tabs can have same chart.. which just makes use of the same interval which is triggered earlier.
Now I have just 1 chart.. But I have many charts to show which are of the same type. Say gauge Chart.
I also have to clear the timeout whenever there is no chart present in the current selected tab - which I am doing.
So I am planning to make just 1 function which just makes the call to the server by passing in the required params to this function.
But in order to poll, I am using window.setTimeout thing I mentioned above.
This works for 1 chart.
Now, I try to add 1 more chart, with different set of params to poll the server, I will need to make use of some different setTimeout function, which has a id different than that of the earlier triggered timeout.
I also have to consider that if the 1st chart is already present, the timeout is already triggered and have to keep it running.
So, now I have to trigger the second timeout.
But there is no second timeout here.
I was wondering if there is any alternate approach to this, as I can't really predict how many chart's there will be on runtime.
Question 1 : Can we flood our browser with many timeout's?
Question 2 : How to get the id of that particular timeout, so that I can clearTimeout(id) on it?
Question 3 : Since we can't assign / make variables on the fly, how to set / make such a data structure which can hold such a pointer to the particular chart's index / id.. so that we can easily get hold of it and clear it.
Question 4 : Is this the only way we can poll the server(via AJAX) if we have to poll continually?
Lastly, I recognize this is a very complex issue I have posted in here. But I am sure I will find some useful information about the approach from the forums.
I don't have much experience doing all these stuffs in JS, but any help is appreciated!
Update
Sorry I have to post my code in here.. But I am using Extjs to get my chart portlets. My code for the function connectToVM is this :
function connectToVM(portalId, host, port, user, passwd, db) {
try{
if(Ext.getCmp(portalId))
{
var gaugeChartForTitle = Ext.getCmp(portalId);
if(typeof portalOriginalTitle === 'undefined')
portalOriginalTitle = gaugeChartForTitle.title;
var gaugeChartDiv = document.getElementById(portalId);
Ext.Ajax.request({
url: "/connectToVM?" +
Ext.urlEncode({
host: host,
port: port,
user: user,
passwd: passwd,
db: db
}),
method: 'GET',
success: function (response, options) {
if(response.responseText !== "")
{
gaugeChartDiv.style.background = "";
gaugeChartForTitle.setTitle(portalOriginalTitle);
console.log("Virtual Machine at "+ host +" : BUSY % : "+response.responseText);
virtualMachineStore.loadData(generateVirtualMachineData(response.responseText)); //Setting the data1 value of the store and loading it for display!
windowInterval = window.setTimeout(function() {
connectToVM(portalId, host, port, user, passwd, db)
}
, 4000);
}
else
{
windowInterval = window.setTimeout(function() {
connectToVM(portalId, host, port, user, passwd, db)
}
, 10000); //Retry every 10 seconds to check if the connection is established!
gaugeChartDiv.style.background = "red";
gaugeChartForTitle.setTitle(portalOriginalTitle +" - Connection Failure. Reconnecting!");
}
},
failure: function ( result, request) {
}
});
}
}
catch(err) {
}
}
Now, I trigger my function using this :
function setWindowIntervalForVM(portalId) {
//console.log("isIntervalActivated inside setWindowIntervalForVM() : "+isIntervalActivated);
if(!isIntervalActivated) {
connectToVM(portalId, host, port, user, pwd, db);
}
}
function checkIfWindowIntervalIsActivated(portal) {
if(!isIntervalActivated) {
setWindowIntervalForVM(portal.id);
isIntervalActivated = true;
} else {
window.clearInterval(windowInterval);
windowInterval = null;
isIntervalActivated = false;
}
}
So checkIfWindowIntervalIsActivated() is my parent function call which I call in these scenarios :
1) Whenever the Gauge Chart is newly created.. I Trigger this call and have a boolean isIntervalActivated which if it is false, triggers the server poll.
2) So now if I have the chart already in tab 1(since the user selected it), I now change to tab 2 which does not have it. So I simply set isIntervalActivated to true which stops the poll. This is handled for 1 chart. Now the question here is, if I want to make this function re-usable, say I want to drop one more chart of same type but with different server parameters to poll, how to make use of the same windowInterval variable which has my 1st chart's triggered timeout value. P.S: The value changes for every ajax request it makes. So there'z no 1 single value :(
3) I stop the poll whenever there is no chart of same type present.. in other tab. which makes perfect sense. Now, I am caching all my portlets whenever user drops in a new portlet / on the page load, pulling all the user configured portlets. In such a case, I have to trigger all of the charts' ajax calls.. each polling to its configured destination. Now, I do not know how many charts there will be, as in my function name, I am polling to VM's. So if the user consumes VM1, it switches to VM2 and so on.
So it's absolutely impossible to just create same function for many such similar charts.
So just wanted to check if I can re-use the same timeOut thing, or take a totally different approach to this problem :( :(
I hope it's a bit clear now, if not I can explain my situation more.
Please ask me more questions if required :)
Thanks again!
If I understood correctly and you're trying to support multiple charts updating concurrently, I'd switch from keeping the chart data inside the connectToVM() closure to an explicit array of chart objects and use a single interval to update all charts.
Something like the following (treat it as pseudo-code):
var charts = [
// an array of chart objects, see addChart()
];
function addChart() {
// when you need to add or remove a chart, update the charts object, like this:
charts.push({
update: updateChart,
nextUpdateTime: null, // or Date.now() if you don't care about old browsers.
chartData: {host: ..., port: ..., user: ..., passwd: ..., db: ...,
originalTitle: ..., portalId: ...},
});
restartUpdates();
}
var activeInterval = null;
function restartUpdates() {
if (activeInterval) {
clearInterval(activeInterval);
}
activeInterval = setInterval(updateCharts, 5000);
}
// updates all active charts
function updateCharts() {
var now = new Date().getTime();
for (var i = 0; i < charts.length; i++) {
var chart = charts[i];
if (chart.nextUpdateTime !== null && chart.nextUpdateTime < now) {
chart.nextUpdateTime = null; // chart.update() will re-set this
try {
chart.update(chart);
} catch(e) {
// handle the error
}
}
}
// update a single chart.
// #param |chart| is an item from the |charts| array.
function updateChart(chart) {
// ...same as your connectToVM() using properties from chart.chartData...
Ext.Ajax.request(
// ...
success: function (response, options) {
// ...same as before...
// ...but instead of re-setting the timeout:
// windowInterval = window.setTimeout(function() {
// connectToVM(portalId, host, port, user, passwd, db)
// }
// , 4000);
// ...update the chart's nextUpdateTime:
chart.nextUpdateTime = (new Date().getTime()) + 4000;
}
);
}
initial answer below
Thanks for the detailed question! It feels you're missing something very obvious wrt questions #2/3, but it's hard to tell what specifically without seeing more of your code. Can you post a more complete, yes simple example demonstrating the problem you're trying to solve? Perhaps the function handling changing the active tab in pseudocode would help, like this:
function selectTab(tabID) {
// ...activate tab #tabID in the GUI...
if (tabID == 1) {
// there's chart #1 on tab #1, need to stop any active timeouts and start a new one
connectToVM("chart #1");
} else if (tabID == 2) {
// no charts on tab #2.. need to stop any active timeouts
} else if (tabID == 3) {
// ...
}
}
One thing I don't understand is whether there's always a single chart, that needs updating, at any point of time?
Also, do you know the concepts mentioned in A re-introduction to JavaScript, specifically objects?
As for the questions:
1: yes, too many timeouts should be avoided (thousands a second will probably make the CPU hot and the browser sluggish), although I'd be more worried about the server, which has to handle the requests from multiple clients.
2/3: see above.
4: The Comet page lists a lot of alternatives to basic AJAX polling (server-sent events, long-polling, websockets), but I'd worry about this later.
Yes
var x = window.setTimeout(...); window.clearTimeout(x);
Store it as a data attribute on the active tab, a property on your object, or as a global variable. Many different ways. Example code would have made it easier to answer this.
Based on your comments:
var windowInterval;
function connectToVM(portal) {
if(windowInterval)window.clearTimeout(windowInterval);
windowInterval = window.setTimeout(function() { ... }, 4000);
}