Develop Reference

Problem with infinite loop when manipulating DOM

I'm learning about DOM manipulation and, to practice, I'm trying to get the first 100 Twitter users who have twitted about #Javascript (see link). As, for now, Twitter doesn't allow you to use console.log() function in the browser console, I have managed to show any string visually in the HTML, in this case, under the search textbox.
This is my "custom" console.log()
function consoleLog(data) {
var searchTextBox = document.querySelector("#doc > div.topbar.js-topbar > div > div > div > div > div");
var p = document.createElement("p");
var innerText = document.createTextNode(data);
p.appendChild(innerText);
searchTextBox.appendChild(p);
}
For getting the usernames, I keep scrolling the page every 4 seconds and looking for usernames until I have 100 or more of them in my usernames variable.
var scrollPage = setInterval(function() {
window.scrollTo(0, document.body.scrollHeight);
}, 4000);
var usernames = [];
while (true) { // <------ PROBLEM
if (usernames.length < 100) {
consoleLog("Getting usernames again");
usernames = getUsernames();
}
else {
consoleLog("We have ENOUGH usernames. BREAK");
clearInterval(scrollPage);
printUsernames();
break;
}
}
function printUsernames() {
for(var user of usernames) {
consoleLog(user);
}
}
function getUsernames() {
var results = [];
var usernameNodes = document.getElementsByClassName("username u-dir u-textTruncate");
var username = usernameNodes[0].textContent;
for(var node of usernameNodes) {
results.push(node.textContent);
}
return results.filter(isUnique);
}
function isUnique(value, index, self) {
return self.indexOf(value) === index;
}
The problem is that the while loop enters in infinte loop and I don't know why. I think the logic of the code is correct. In fact, if I first copy and paste all the declared functions to the browser console, then start the scrollPage interval and, lastly, start the while loop, it works well. The problem comes when I copy and paste all the code at one time in the browser console. It is like the executions of the interval and the while loop conflict in some way. But I can't understand.

Its better to have while conditioned like this:
var usernames = [];
// This will automatically end when length is greater or equall 100
// no need to break
while (usernames.length < 100) {
consoleLog("Getting usernames again");
usernames = getUsernames();
}
consoleLog("We have ENOUGH usernames.");
clearInterval(scrollPage);
printUsernames();

Javascript HTML include results in duplicate includes in random places

This problem has me absolutely stumped. I'm trying to include HTML snippets with Javascript and it works, but for some reason it decides to also include duplicate snippets in various other locations.
Here is a screenshot of what I mean:
It also varies the number and location of these random includes.
This is the function I use to include. It searches through the document and finds div elements with the attribute include="x.html"
function include() {
var allElements;
var fileName;
var includeRequest;
allElements = document.getElementsByTagName("*");
for (var i = 0; i < allElements.length; i++) {
if (allElements[i].getAttribute("include")) {
fileName = allElements[i].getAttribute("include");
includeRequest = new XMLHttpRequest();
includeRequest.open("GET", fileName, true);
includeRequest.onreadystatechange = function() {
if (includeRequest.readyState == 4 && includeRequest.status == 200) {
allElements[i].removeAttribute("include");
allElements[i].innerHTML = includeRequest.responseText;
include();
delete includeRequest;
includeRequest = null;
}
}
includeRequest.send();
return;
}
}
}
This is the function that gets tags from an html file containing articles, and adds them to the list of tags in the box on the right. As you can see, in one place the footer is added to the list instead of the tag. I don't know why.
function getTags() {
var taglist = document.getElementById("taglist");
var tagsRequest = new XMLHttpRequest();
tagsRequest.open("GET", "blogstubs.html", true);
tagsRequest.responseType = "document";
tagsRequest.onreadystatechange = function() {
if (tagsRequest.readyState == 4 && tagsRequest.status == 200) {
var tagsResponse = tagsRequest.responseXML;
var tags = tagsResponse.getElementsByClassName("tag");
var tags = getUnique(tags);
var len = tags.length;
for (var i = 0; i < len; i++) {
var li = document.createElement("li");
li.appendChild(tags[i]);
taglist.appendChild(li);
}
delete tagsRequest;
tagsRequest = null;
}
}
tagsRequest.send();
}
Javascript only solution please. Ideas?

I copied your website (I hope you don't mind) and tested it with my changes, it seems to be working now without this bug. Here's what I did:
1) I created a new function, don't forget to change the name to whatever you prefer:
function newFunction(allElements, includeRequest) {
allElements.removeAttribute("include");
allElements.innerHTML = includeRequest.responseText;
include();
delete includeRequest;
includeRequest = null;
}
2) I changed the include() function to look like this:
function include() {
var allElements;
var fileName;
var includeRequest;
allElements = document.getElementsByTagName("*");
for (var i = 0; i < allElements.length; i++) {
if (allElements[i].getAttribute("include")) {
var element = allElements[i];
fileName = element.getAttribute("include");
includeRequest = new XMLHttpRequest();
includeRequest.open("GET", fileName, true);
includeRequest.onreadystatechange = function() {
if (includeRequest.readyState == 4 && includeRequest.status == 200) {
return newFunction(element, includeRequest);
}
}
includeRequest.send();
return;
}
}
}
I think the problem was caused by async nature of AJAX requests, like I said in the comment. So you need to pass the variables to your AJAX call instead of using the global scope, that's why you need this new callback function.
In other words, in the original code the AJAX variable allElements[i] wasn't in sync with your loop's allElements[i], so while in your loop it would be 5, in AJAX function (which executed separately and not in order with the loop) it would be 3, 6 or whatever else. That is why it would append the html to the element that seems random. Think of AJAX as of someone who doesn't care about the order of your loops, someone who really doesn't like to wait while someone else is counting and does everything in his own order.

Can't update javaScript global variable

Here I have global variable userId, and i want to update it inside signInUserFunction(), to use is in other function. I have tried to define it using var, window, But all these didn't help. This variable doesn't update. As i see its about AJAX async. So, what can i do with it?
And yes, I know that its not good to make authentication with JS, I am quite new to it. So, I am just creating random methods to improve.
var userId = 1;
function signInUser() {
$.getJSON('http://localhost:8887/JAXRSService/webresources/generic/getAllUsers', function(data) {
var items = [];
var i = 0;
$.each(data, function(firstname, value) {
var str = JSON.stringify(value);
data = JSON.parse(str);
var innerId;
for (p in data) {
innerId = data[p].id;
if ($('#nameSignIn').val() == data[p].first_name && $('#passwordSignIn').val() == data[p].password) { //
userId = innerId;
window.location.href = "content.html";
break;
} else {
i++;
if (i == data.length) {
alert("Ощибка в логине или пароле!")
}
}
}
});
});
}

How are you determining whether or not it has been set? It looks like immediately after you set it, you navigate to a different page. When you get to that page, you will have an entirely new window.
Try alerting the value before navigating away.
EDITED: Here is how you could pass it to the other page (but you shouldn't do this in a real app)
window.userId=innerId;
alert(window.userId);
//this isn't a very secure way to do this. I DON'T recommend this
window.location.href = "content.html?id=" + innerId ;
Then in the other page, you could access it off the document.location:
alert(document.location.toString().split("?id=")[1]);

After reading my comments, you may want to try this:
var userId = 1;
function signInUser(){
$.getJSON('http://localhost:8887/JAXRSService/webresources/generic/getAllUsers', function(data){
var items = [], actors = data.Actors, l = 0;
$.each(actors, function(i, o){
l++;
if($('#nameSignIn').val() === o.first_name && $('#passwordSignIn').val() === o.password){
userId = o.id;
// this will redirect before any other code runs -> location = 'content.html';
if(l === actors.length){
alert('End of Loop');
}
}
});
});
}
signInUser();
I would not store sensitive data in JSON such as passwords. Use a database. There is no need to get all the data at the same time either.

Using the idea #mcgraphix proposed (and giving you the same warning...this would certainly not be the way to transfer data like this in a production environment), here is one way to do it:
function signInUser() {
var url = 'http://localhost:8887/JAXRSService/webresources/generic/getAllUsers';
var userId;
$.getJSON(url, function(data) {
$.each(data.Actors, function(index, actor) {
// Cache the values of the #nameSignIn and #passwordSignIn elements
var name = $('#nameSignIn').val();
var password = $('#passwordSignIn').val();
if (actor.first_name === name && actor.password === password) {
// We have found the correct actor.
// Extract its ID and assign it to userId.
userId = actor.id;
window.location.href = "content.html?userId=" + userId;
}
});
// This alert should only be reached if none of the actor objects
// has a name and password that matches your input box values.
alert("Ощибка в логине или пароле!");
});
}
// On the next page...
// Top answer from http://stackoverflow.com/questions/2090551/parse-query-string-in-javascript
// This approach can handle URLs with more than one query parameter,
// which you may potentially add in the future.
function getQueryVariable(variable) {
var query = window.location.search.substring(1);
var vars = query.split('&');
for (var i = 0; i < vars.length; i++) {
var pair = vars[i].split('=');
if (decodeURIComponent(pair[0]) == variable) {
return decodeURIComponent(pair[1]);
}
}
console.log('Query variable %s not found', variable);
}
var userId = getQueryVariable('userId');

Thanks you for help.Ended it all with usage of:
sessionStorage.getItem('label')
sessionStorage.setItem('label', 'value')

IE8 long running script error when using DataTables

I have an application that uses the DataTables jQuery library to render content in my target browser IE8. The problem is when I push a big array to be rendered, IE8 sometimes throws up the infamous long running script error.
After profiling the app it seems that the call to __fnAddData in the following code is causing the problem:
if (bUsePassedData) {
for (var i = 0, len = oInit.aaData.length; i < len; i++) {
_fnAddData(oSettings, oInit.aaData[i]);
}
} else if (oSettings.bDeferLoading ||
(oSettings.sAjaxSource === null && oSettings.ajax === null)) {
_fnAddTr(oSettings, $(oSettings.nTBody).children('tr'));
}
I was looking around for solutions and saw Nicholas Zakas' write up here and tons of other solutions that would work if the for loop wasn't inside of an if else if "block". When I tried, on my 1st attempt of many, to wrap it in a setTimeout function it of course didn't work because the 2nd part of the if else if resolves to true.
(oSettings.sAjaxSource === null && oSettings.ajax === null) // true
What is a good solution for this? Thanks in advance.

I think you might split up your function in 3 functions:
Before the if statement.
Processing the oInit.aaData
After the if statement
Here is the code split up in 3 functions:
function beforeIf(){
if (bUsePassedData) {
procesData(oSettings,oInit.aaData.concat());
} else if (oSettings.bDeferLoading ||
(oSettings.sAjaxSource === null && oSettings.ajax === null)) {
_fnAddTr(oSettings, $(oSettings.nTBody).children('tr'));
}
afterIF();
}
function processData(oSettings,arr){
//process in chuncks of 50;
// setTimeout takes a long time in IE
// it'll noticibly slow donw your script when
// only processing one item at the time
var tmp=arr.splice(0,50);
for (var i = 0, len = tmp.length; i < len; i++) {
_fnAddData(oSettings, tmp[i]);
}
if(arr.length!==0){
setTimeout(function(){
processData(oSettings,arr);
},0);
return;
}
afterIf();
}
function afterIf(){
//continue processing
}

Thanks #HMR. You helped to bring me closer to my goal. To solve the problem I worked my code down to this IIFE:
(function processData(oSettings, arr) {
var tmp = arr.splice(0, 50);
tickApp.$orders.dataTable().fnAddData(tmp);
if (arr.length !== 0) {
setTimeout(function () {
processData(oSettings, arr);
}, 0);
}
}(oSettings, oInit.aaData.concat()));
Instead of using the private _fnAddData function I opted for the DataTables public fnAddData (http://datatables.net/ref#fnAddData) function. This way I am able to push 50 rows at a time into the table which is stored in the tickApp.$orders object which I just a reference to my jQuery object that stores the table in memory:
tickApp.$orders = $('#orders');
In another part of my code. They way you had it it was still pushing 1 row at a time instead of the whole 50.
Thanks again.

If you are using ajax to fetch your data, you can override "fnServerData" in your datatables config object. This will allow you to fetch the data to be loaded and then process it however you want.
In my case, I have a generic datatables config object that I use for all my datatables. I override the default fnServerData function with one that passes rows to the datatable in sets of 200 using fnAddData and setTimeout to call the function again until all the data has been processed, finally I call fnDraw to draw the table.
var DEFAULT_CHUNK_SIZE = 200;
function feedDataToDataTableInChunks(startIndex, data, oSettings) {
var chunk = data.slice(startIndex, DEFAULT_CHUNK_SIZE);
oSettings.oInstance.fnAddData(chunk, false);
if((startIndex += DEFAULT_CHUNK_SIZE) < data.length) {
setTimeout(function () {
feedDataToDataTableInChunks(startIndex, data, oSettings);
});
} else {
oSettings.oApi._fnInitComplete(oSettings, data);
oSettings.oInstance.fnDraw();
}
}
var config = {fnServerData: function(){
oSettings.jqXHR = $.getJSON(sSource, aoData)
.done(function (result) {
feedDataToDataTableInChunks(0, result || [], oSettings);
});
}}
I am using datatables version 1.9.4

Adding rows to a sqlite database using a loop (Phonegap)

I have created a little Phonegap application that gets news data from an Ajax call via XML. This works fine, but I would like to store the data in a database table to also allow offline reading of the news.
So when the Ajax callback loops through the data, I fill a global news object with it and then call a function to check if the data is already stored in the database. If not, it should be inserted into the database news table.
The problem is that the in the transaction to store the news in the table, it seems like my news Object is not present anymore because I get the message:
Uncaught TypeError: Cannot read property 'title' of undefined in ...
So how can I make sure that this work? Here is the code of the part where I select the news and want to check if it's already there:
// Check if a news from the internet already exists in the database; If not, insert it
function checkNewsInDB(){
db.transaction(function(tx){
tx.executeSql("SELECT * FROM NEWS", [], checkSuccess, dbErrorCB);
}, dbErrorCB, dbSuccessCB);
}
// Result Callback from the News Check
function checkSuccess(ctx, result){
var len = result.rows.length;
var found = false;
for(var n = 0; n < newsContainer.length; n++){
for(var r = 0; r < len; r++){
if(result.rows.item(r).n_title == newsContainer[n].title
&& result.rows.item(r).n_pubdate == newsContainer[n].pubdate){
found = r;
}
}
if(found == false){
db.transaction(function(tx){
tx.executeSql("INSERT INTO NEWS (n_title, n_link, n_creator, n_pubdate, n_description) VALUES (?,?,?,?,?)", [newsContainer[n].title, newsContainer[n].link, newsContainer[n].creator, newsContainer[n].pubdate, newsContainer[n].description], insertSuccess, dbErrorCB);
}, dbErrorCB, dbSuccessCB);
} else {
found = false;
}
}
}
The newsContainer IS filled with a few rows of data, I have checked that. I would be very happy if somebody could help me understand why this does not work.
Thanks in advance!
Greetings,
Bernd

db.transaction is asynchronous - by the time executeSql actually runs, n has already been incremented to the end of the loop.
Rather than creating a new transaction for each item, try moving the loop inside the transaction function.

Thanks for the answer. Here is the code that works for all people who have the same problem:
// Check if a news from the internet already exists in the database; If not, insert it
function checkNewsInDB(){
db.transaction(function(tx){
tx.executeSql("SELECT * FROM NEWS", [], checkSuccess, dbErrorCB);
}, dbErrorCB, dbSuccessCB);
}
// Result Callback from the News Check
function checkSuccess(ctx, result){
var len = result.rows.length;
var found = false;
for(var n = 0; n < newsContainer.length; n++){
for(var r = 0; r < len; r++){
if(result.rows.item(r).n_title == newsContainer[n].title
&& result.rows.item(r).n_pubdate == newsContainer[n].pubdate){
found = r;
}
}
if(found == false){
var title = newsContainer[n].title;
var link = newsContainer[n].link;
var creator = newsContainer[n].creator;
var pubdate = newsContainer[n].pubdate;
var description = newsContainer[n].description;
ctx.executeSql("INSERT INTO NEWS (n_title, n_link, n_creator, n_pubdate, n_description) VALUES (?,?,?,?,?)",
[title, link, creator, pubdate, description], insertSuccess, dbErrorCB);
} else {
found = false;
}
}
}