Develop Reference

Array.from() with HTMLcollection does not seem to work in Chrome browser

I have a JavaScript piece of code that works on all browsers (even IE) but fail with Chrome on my HUAWEI P8 Lite with Android 6.
Chrome is version 71.0.3578.99.
The faulty code is var class_arr = Array.from(class); where class is a HTMLcollection.
It seems like Array.from() is failing although it should be supported by Chrome on mobile.
Also, I've noticed that this same code used to work one update ago, and not two updates ago strangely.
You can test the problem with this URL (of course this won't be valid as long as if I'll find a solution to my problem). You need to open the sidebar on the left and try to zoom in the map with the Plus or Minus button.
EDIT
Here is the code where I use Array.from():
export function updateSlider(all_sliders, ol_layers, class_layers) {
// updates slider with the actual opacity of the layers
for (var i = 0, len_i = all_sliders.length; i < len_i; ++i) {
var curr_slider = all_sliders[i];
// get layer from ol_layers whose title is equal to current slider id
// Find the value of the first element/object in the array, otherwise undefined is returned
// (https://stackoverflow.com/a/13964186/1979665)
var lyr = ol_layers.find(obj => {
return obj.values_["title"] === curr_slider.getAttribute("id")
});
// get class_layer (layerswitcher) from class_layers whose title is equal to current slider id
// (first we need to convert class_layers from HTMLCollection to array otherwise .find will fail)
var class_layers_arr = Array.from(class_layers);
var class_elem = class_layers_arr.find(obj => {
return obj.innerText.replace('\t','') === curr_slider.getAttribute("id")
});
// get current layer opacity and set it as the value of current slider
var curr_opacity = lyr.values_["opacity"];
curr_slider.setAttribute("value", curr_opacity);
// create new li element
var li_elem = document.createElement("LI");
// add slider input to li elem
li_elem.appendChild(curr_slider);
// add li with layer legend after layer li
insertAfter(li_elem, class_elem);
changeOpacity(curr_slider, ol_layers);
}
}
class_layers is first defined in another script as var class_layers = document.getElementsByClassName("layer");
EDIT 2
Ok, so apparently the problem is related to Chrome in general, not only on mobile. In fact, if you try the above URL in Chrome Desktop, you can reproduce the error by opening the sidebar (on the left), then closing it and pressing the + or - symbol to zoom in the map. I guess it has to do with the way click events are treated by either my code and OpenLayers. I am probably deleting this question as it sounds like I need to dig further in problematic.
SOLUTION
Not deleting because I think it maybe useful for others to see the solution.
Here is the link to the OpenLayers github issue I created and closed: https://github.com/openlayers/openlayers/issues/9105.
The problem was the event "change:resolution" fired by the View class of OL (v5.3.0) that is emitted multiple times during animation (problem also quoted here).
NEW CONSIDERATION
Turns out that I still had the problem on mobile devices.
The real fix was not to use innerText in my code and switch to innerHTML, as it was always empty in (and only in) Chrome, while with the other browsers it was not (I could actually see the string). If you are interested I can try to provide an example, but unfortunately I could not find much on this problem in the web...

It's not Array.from() problem.
Check your class_elem variable
It's undefined (because no element found for your conditions) and then it fails when your trying to get parentNode of undefined in:
export function insertAfter(newNode, referenceNode) {
referenceNode.parentNode.insertBefore(newNode, referenceNode.nextSibling);
}

jQuery append fails on first pass of for loop (but succeeds on others)

I'm using a for loop to iterate through data from a weather API. Within that for loop, I'm assigning each night a rating on its suitability for stargazing (var totalRanking). Then I update a series of divs, having IDs day0, day1, etc., with this rating. (If it matters, these divs are being generated dynamically.) Here's the code block in question:
var dayRankLine = $("<div>");
var rating = $("<span class=rating>"); // happens
rating.text(Math.round(totalRanking * 100) + "%"); // happens
dayRankLine.html("Score: "); // happens
dayRankLine.append(rating); // doesn't happen on 0. (does on others)
$("#day" + i).after(dayRankLine); // happens (even on 0)
As shown in the comments, the first div, #day0, is getting text Score:, but no number. The remaining divs are working as expected. A later code block uses the rating for day 0 to update a different DOM element, and works as expected, showing that the correct value is getting input.
What's different about the first iteration through the loop, and what's different about appending, that that line should fail on that pass only?

Ohhh nevermind. As I said, I was using rating in a lower code block, and that was "stealing" it from day0. rating.clone() and problem solved.

How can I remove blank lines in an array generated that show in a dropdown

I have a dropdown that is generated using javascript and html. I have some code which I will post below that loops through this list and should potentially remove any blank lines found but is not working. "$maxfield1rows" has a value of 7, what I am saying is that if the value is a blank (=='') then remove it. I used removeChild but this doesn't seem to work, I also tried splice, I think filter can work but am not sure. I tried the disabled=true but that just makes them disabled and unselectable. Can someone please help?
for(index=1; index<$maxfield1rows; index++) {
if(document.pickDivision.field1.options[index].value=='') {
document.pickDivision.field1.removeChild(document.pickDivision.field1.options[index]);
}
}
Updated below, I'm using $maxfield1rows since that is the amount of maximum number of rows the the loop goes through, also by change I meant that there is an onchange event that gets triggered when the user selects a different option in the dropdown menu, so depending on the option selected the output for field1 changes, sometimes there are 5 values that show and sometimes just 1:
for(index=$maxfield1rows-1; index>=0; index--) {
alert(document.pickDivision.field1.options[index]);
if(document.pickDivision.field1.options[index].value==''){
document.pickDivision.field1.removeChild(document.pickDivision.field1.options[index]);
document.pickDivision.field1.options[index].disabled=true;
}
else{
document.pickDivision.field1.options[index].disabled=false;
}
}

To expand upon my comment, I think the issue is that you are looping forwards through the options array. I am surprised that no error is being thrown when you try to do this. You should loop backwards through the collection to keep from skipping an item.
JS Fiddle demonstrating the error. In the example, items 1 and 2 are blank and item 3 is not.
These built in collections are changed each time your add/remove an item. Using the example in the fiddle, my array changes from [1,2,3] to [2,3] to error no item at index 2.
Looping backwards, my collection takes this change: [1,2,3] to [1,3] to [3].
Here is the code with comments explaining what each part of the for loop is used for and why. You can use a while loop if you prefer too.
//options.length - 1 because arrays are 0 based
//i >= 0 because you don't want to use a negative index on an array
//i-- to loop backwards
for(var i = document.pickDivision.field1.options.length - 1; i >= 0; i--) {
//Is this an empty item
if(document.pickDivision.field1.options[i].value == '') {
//Remove the empty item
document.pickDivision.field1.removeChild(document.pickDivision.field1.options[i]);
}
}
UPDATE
With the newly updated code you posted, you are attempting to access an option element after it has been removed. From the looks of the line, you don't need it anymore as you are already removing the element. If you do still want to disable the element before removing it, move that line above the other line (see comment in code).
for(index=$maxfield1rows-1; index>=0; index--) {
alert(document.pickDivision.field1.options[index]);
if(document.pickDivision.field1.options[index].value==''){
document.pickDivision.field1.removeChild(document.pickDivision.field1.options[index]);
//This line is causing the issue; move it above the previous line or remove it
document.pickDivision.field1.options[index].disabled=true;
}
else{
document.pickDivision.field1.options[index].disabled=false;
}
}
UPDATE 2
Per the question in the comments, when you change the number of options to 6, your code breaks. This is because you are using the hard coded PHP value $maxfield1rows. Since you already know the name of the form and the name of the field in the form, I would recommend you use the length of the options collection in your for loop rather than this variable. This will make sure that no matter how many option elements there are (1, 10, 1000), you will always loop through the entire collection.
for(var i = document.pickDivision.field1.options.length - 1; i >= 0; i--) {

slideshow counter disappears

I have this code that is supposed to generate a counter for a slideshow and then change the picture and the corresponding number color in the counter. However, after the slideshow cycles through twice, the counter changes to display:none and then reappears and disappears every time the slideshow begins its cycle.
//icons for newsreel guide
for(i=0;i<document.getElementsByClassName("news").length;i++){
var count=i+1;
$('#counter').append('<span class="count">'+count+'</span>');
}
//newsreel script
$(".news").hide();
setTimeout (function() {
var wait = $(".news:last").index()*12000+12000;
function newsreel(){
var i=0;
(function showNews(elem){
if(i==document.getElementsByClassName("count").length){
i=0;
}
document.getElementsByClassName("count")[i].style.color="#000";
elem.fadeIn(2000,function(){
elem.delay(8000).fadeOut(2000,function(){
document.getElementsByClassName("count")[i].style.color="#3159a0";
i=i+1;
$(this).next().length && showNews($(this).next());
});
});
})
( $(".news:first"));
setTimeout (arguments.callee, wait);
}/*end newsreel()*/
newsreel();
}, 2000);
At first I thought it was using the deprecated arguments.callee but I changed that and it still happens on cue. Any ideas?

I checked your code, and the problem is in this line :
$(this).next().length && showNews($(this).next())
.next() is getting the next sibling. Your counter is a sibling of .news. To solve your problem, do this:
$(this).next().length && showNews($(this).next('.news'))
That will select the next sibling with the class news.

I suspect it's because your showNews function is never running. I think the JavaScript engine is evaluating
(function showNews(elem){
//...
})
and
( $(".news:first"));
as two different expressions, rather than passing $(".news:first") as a parameter to showNews as you intend. Since ; at the end of a line is optional in JS, the parser will insert one automatically if the result is valid JavaScript. In this case, it defines a function but never calls it, then builds a jQuery sequence but never uses it.
Try removing the carriage return between the two:
(function showNews(elem){
//...
})($(".news:first"));

Improving performance of javascript intervals on IE8

I'm using javascript loop (using setInterval) that runs through a list of search results, highlighting the search term by adding a css styled <span> around search hits as it goes. I'm using setInterval like this to release control of the browser while it does this.
In Chrome and Firefox this works well - even with a setInterval parameter of 10-20ms; and the user has full control of the browser (i.e. scrolling, clicking links etc.) while the results are rapidly highlighted:
mylooper = setInterval(function() {
// my functionality is here
},15); // 15ms
Unfortunately, when using the dreaded IE8, the browser locks up and takes a really long time to add the <span>'s and style the search results. It also takes a long time just to load the page in the first place - shortened a great deal when this script is removed.
So far I've tried:
changing the interval values (I've read that IE8 doesn't detect intervals of sub 15ms);
using setTimeout instead of setInterval;
removing the interval to check that this is in fact what is causing the slow-down (it is!); and
swearing about Internet Explorer a lot;
var highlightLoop;
var index = 0;
highlightLoop = setInterval(function () {
var regex = RegExp(regexPhrase, "gi"); // regexPhase created elsewhere
var searchResults = resultElements.eq(index).get(0); // run through resultElements which contain alll the nodes with search results in them.
findAndReplaceDOMText( // a function that does the searching and inserting of styling
regex,
searchResults,
function (fill, matchIndex) {
called = true;
var span = document.createElement("span");
span.className = "result-highlight";
span.innerHTML = fill;
return span;
}
);
if (index == resultElements.length || searchTermUpdated == true) { // stop interval loop when search term changes or we reach the end of results - variable set elsewhere.
searchTermUpdated = false;
clearInterval(highlightLoop); // stop the loop
}
index++
}
}, 50); // 50ms does not improve performance.
Any advice on workarounds for this kind of javascripting in IE would be massively appreciated. Thanks all.

I believe you may be able to improve the performance by tweaking findAndReplaceDOMText, and maybe its callback too. I suppose findAndReplaceDOMText appends the element returned by the callback to the DOM, from within a loop of all matches. If it's doing that inside a loop, try to move it outside the loop, and apply the all changes to the DOM at once. That should result in better performance, as repainting the page after each DOM update is expensive.

Try this recursive approach instead:
get a list of all elements to be acted upon into array X (one time cost)
while the array X has length, keep repeating the next actions
shift the first element off the array
process the single element
start this process again with the new array X (now Xn - 1 length) on a setTimeout
The code looks like this in general
function processArray(array) {
var element = array.shift();
processElement(element);
if (array)
setTimeout(function(){processArray(array);},15ms);
}
There might be something else to be done with this recursion, but it works fairly well in all browsers and never blocks, because you're only initiating the repeat when the last one has had time to finish.