I need this code to find all URL's from several webpages and list them in a certain order in console. I need the list to begin with URL's from fakeURL.com/0 and end with fakeURL.com/20, and stay in order all the way. The problem is that sometimes it will list URL's from (for example) fakeURL.com/5 before URL's from fakeURL.com/2.
It also needs to be in order within each webpage - URL's that are more near the top of a webpage should come first.
What's causing the list to be out of order, and how can I fix it?
var i;
function ajaxCall (x)
{
var xhrs = new XMLHttpRequest();
xhrs.open("get", 'http://fakeURL.com/' + x, true);
xhrs.onload = function()
{
var doc = xhrs.response;
$(doc).find('a').each(function()
{
var url = $(this).attr('href');
console.log(url);
});
}
xhrs.responseType = 'document';
xhrs.send();
}
for(i = 0; i <= 20; i++)
{
ajaxCall(i);
}
The XMLHttpRequest by default is asyncronous. So, if you call ajaxCall() with 1,2,3,...20 (for your particular case) this doesn't guarantee you that the URL is printed (console.log) in the same sequence.
For more information, read this documentation from mozilla
The reason why you get the values out of order despite traversing incrementally in a for loop is because that's how an XMLHttpRequest works by default (i.e. asynchronously)
From the official documentation, in an Asynchronous HTTP Request, the elements don't freeze while the request happens in the background and once the resources are fetched, you can tap on them by using a callback function.
Synchronous requests block the execution of code which creates "freezing" on the screen and an unresponsive user experience.
So Sychronous requests might seem the way to go in your case, but they have performance implications and of course may account for a bad user experience.
A simple work around that I can suggest for your case which I understand is just listing the URLs, is just let the URLs get fetched in whatever way they want to. Store them in an array and add another attribute to them called page_id or something that can help you identify the order of your links. So the outermost links could look something like:
var a = {link: "http://fakeURL.com/1", page_id: 1};
//Store such objects in a list.
For internal links on one page as well, let them get parsed in whatever they want to, and just associate their indices with them using .index() in Jquery. From the documentation:
//html
<ul>
<li id="foo">foo</li>
<li id="bar">bar</li>
<li id="baz">baz</li>
</ul>
//Javascript
var listItem = document.getElementById( "bar" );
alert( "Index: " + $( "li" ).index( listItem ) );
//Outputs - Index: 1
Now when you need to display the links, just sort the relevant lists with the page_id attribute or the depth attribute and display them accordingly. Hope it gets you started in the right direction.
Related
Messing around with an autocomplete plugin available at https://www.npmjs.com/package/bootstrap-4-autocomplete, and the following works:
$('#id').autocomplete({
source: {'test1':1, 'test2':2, 'test1':3}
});
Instead of local JSON, will need to make an XMLHttpRequest and was thinking something like the following, and while I don't get an error, I also don't get anything:
$('#id').autocomplete({
source: function() {
var xhttp = new XMLHttpRequest();
xhttp.onreadystatechange = function() {
if (this.readyState == 4 && this.status == 200) {
return JSON.parse(this.responseText);
}
};
xhttp.open(method, url, true);
xhttp.send();
}
});
The plugin's author made the following remark a while back:
I don't have plans to directly invoke any url inside the lib. What you
can do is set autocomplete to your textfield after your ajax call
returns, which you can do with jQuery, like this:
$.ajax('myurl').then((data) => $('#myTextfield').autocomplete({
source: data }));
You don't have to worry about setting autocomplete to a field multiple
times, it is supposed to work like this when you need to change the
source.
Tried it and as expected, $.ajax() initiated an XMLHttpRequest request upon page load, and not as desired when the user enters a character into the search input.
How am I able to make an XMLHttpRequest to source the data into the plugin? I am assuming that I should be using a promise, however, if not, still would appreciate any assistance.
Thanks
Well, that's how plugin supposed to work. Its meat and potatoes is createItems function, called on keyup event - and responsible for filling out that dropdown with items. And here's its key part (1.3.0 version):
function createItems(field: JQuery < HTMLElement > , opts: AutocompleteOptions) {
const lookup = field.val() as string;
// ...
let count = 0;
const keys = Object.keys(opts.source);
for (let i = 0; i < keys.length; i++) {
const key = keys[i];
const object = opts.source[key];
const item = {
label: opts.label ? object[opts.label] : key,
value: opts.value ? object[opts.value] : object,
};
if (item.label.toLowerCase().indexOf(lookup.toLowerCase()) >= 0) {
items.append(createItem(lookup, item, opts));
if (opts.maximumItems > 0 && ++count >= opts.maximumItems) {
break;
}
}
}
// skipped the rest
}
As you can see, each time createItems is called, it goes through source object, grepping all the items containing lookup string.
So all the data parts are expected to be there - and to be processable synchronously. That's the plugin's way, with all good and bad coming out of this approach.
The best thing the plugin's author could've suggested here (without going against what plugin is about) is using AJAX to prepopulate the data before calling autocomplete. And that's what he did in that comment actually.
Now, what can be done here? One might think it's enough just to transform createItems into an async function - for example, calling source if it's a function and expecting its result to be a Promise. It seems to be seductively simple excluding that lookup loop in process - and just take the the results of that AJAX call to repopulate source...
But that's not so simple, unfortunately: there are several caveats to be aware of. What should happen, for example, if user stops typing (triggering first AJAX call), then types some more, then stops once again (triggering another AJAX call) - but the first one actually arrives later? The corresponding bug was plaguing a lot of autocomplete implementations I've been working with, sadly - it's not that easy to reproduce if you're testing only with fast network connections (let alone only on localhost).
That's just one of the reasons the author decided against extending that plugin, it seems. After all, it was built to solve one specific task - and it does this well. So unless you want to fork it and essentially rewrite it into 'two strategies' one, I'd suggest considering looking somewhere else.
I have recreated a blueprint, which has 60+ rooms, as an inline SVG.
There are functions that display information, such as pictures, when you select or hover a room. I'm using one div container to display the pictures by setting its background property to url('path-of-image.ext'), as can be seen below.
var cla = document.getElementsByClassName('cla');
for (i = 0; i < cla.length; i++) {
cla[i].addEventListener('mouseenter', fun);
}
function fun(){
var str = 'url("media/' + this.id.slice(4) + '.jpg")';
pictureFrame.style.background = str;
pictureFrame.style.backgroundSize = 'cover';
pictureFrame.style.backgroundPosition = 'center'
}
The reason I'm not using the background property's shorthand is because I plan on animating the background-position property with a transition.
However, not all rooms have pictures. Hence console throws the following error, GET ... net::ERR_FILE_NOT_FOUND, when you select or hover said rooms. The error doesn't cause the script to break, but I would prefer not to run that code every single time a room is hovered, even when a given room doesn't have pictures.
Even though I know this can be done imperatively with if/else statements, I'm trying to do this programmatically since there are so many individual rooms.
I've tried using try/catch, but this doesn't seem to detect this sort of error.
Any ideas?
Is it even possible to detect this kind of error?
You could attempt to read it using FileReader and catch/handle NotFoundError error.
If it were to error, you could assign it to an object or array which you would first check upon hover. If the file was in that array, you could avoid attempting to read it again and just handle however you like.
Here is a good article by Nicholas Zakas on using FileReader
First off I would see if there is a way of checking if the file exists before the document even loads so that you don't make unnecessary requests. If you have a database on the backend which can manage this that would serve you very well in the long term
Since you make it sound like the way you only know a file exists is by requesting it, here's a method that will allow you to try this:
function UrlExists(url)
{
var http = new XMLHttpRequest();
http.open('HEAD', url, false);
http.send();
return http.status!=404;
}
This won't request the image twice because of browser caching. As you can see that method is itself being depricated and overall the best way you can remedy this problem is checking before the page even loads; if you have a database or datastructure of any sort, add a class or property to the element if the image exists or not. Then, in your existing method, you can call something like document.getElementsByClassName('cla-with-image') to get only records that you've determined has an image (much more efficient than trying to load images that don't exist).
If you end up using that UrlExists method, then you can just modify your existing method to be
function fun(){
var url = "media/' + this.id.slice(4) + '.jpg";
if (UrlExists(url)) {
var str = 'url(' + url + ')';
pictureFrame.style.background = str;
pictureFrame.style.backgroundSize = 'cover';
pictureFrame.style.backgroundPosition = 'center'
}
}
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 have an <a> tag which I'm using to redirect the user to another xpage.
Its href property is:
<a target="_blank" href="http://serv/MyBase.nsf">
I use a simple view listing a doc. which contains the server and the name of the application.
So, I want to use some #DbLookup function in javascript to get into 2 var the above server and app name:
var server = #Unique(#DbColumn(#DbName(), "myVw", 1);
var name = #Unique(#DbColumn(#DbName(), "myVw", 2);
var concat = server+"/"+name;
return concat;
How can I compute the href property to return the concat variable?
Create a Link control xp:link and calculate the URL in attribute value:
<xp:this.value><![CDATA[#{javascript:var server .... }]]></xp:this.value>
Knut's approach is correct, but your code isn't :-). For every XPages load (or refresh) you do 4 #DbLookup. You can do a set of optimisations here:
Combine the result you want in the view itself, so you only need one lookup
Cache the value in the session (or application scope)
something like this (add nice error handling):
if (sessionScope.myHref) {
// Actually do nothing here
} else {
sessionScope.myHref = #Unique(#DbColumn(#DbName(), "myVw", 3);
}
return sessionScope.myHref;
The 3rd column would have the concatenation in the view already. That little snippet does a lookup only once per session. If it is the same for all users, use the applicationScope then it is even less.
No idea what I'm doing or why it isn't working. Clearly not using the right method and probably won't use the right language to explain the problem..
Photogallery... Trying to have a single html page... it has links to images... buttons on the page 'aim to' modify the path to the images by finding the name currently in the path and replacing it with the name of the gallery corresponding to the button the user clicked on...
example:
GALLERY2go : function(e) {
if(GalleryID!="landscapes")
{
var find = ''+ findGalleryID()+'';
var repl = "landscapes";
var page = document.body.innerHTML;
while (page.indexOf(find) >= 0) {
var i = page.indexOf(find);
var j = find.length;
page = page.substr(0,i) + repl + page.substr(i+j);
document.body.innerHTML = page;
var GalleryID = "landscapes";
}
}
},
There's a function higher up the page to get var find to take the value of var GalleryID:
var GalleryID = "portfolio";
function findGalleryID() {
return GalleryID
}
Clearly the first varGalleryID is global (t'was there to set a default value should I have been able to find a way of referring to it onLoad) and the one inside the function is cleared at the end of the function (I've read that much). But I don't know what any of this means.
The code, given its frailties or otherwise ridiculousness, actually does change all of the image links (and absolutely everything else called "portfolio") in the html page - hence "portfolio" becomes "landscapes"... the path to the images changes and they all update... As a JavaScript beginner I was pretty chuffed to see it worked. But you can't click on another gallery button because it's stuck in a loop of some sort. In fact, after you click the button you can't click on anything else and all of the rest of the JavaScript functionality is buggered. Perhaps I've introduced some kind of loop it never exits. If you click on portfolio when you're in portfolio you crash the browser! Anyway I'm well aware that 'my cobbled together solution' is not how it would be done by someone with any experience in writing code. They'd probably use something else with a different name that takes another lifetime to learn. I don't think I can use getElement by and refer to the class/id name and parse the filename [using lots of words I don't at all understand] because of the implications on the other parts of the script. I've tried using a div wrapper and code to launch a child html doc and that come in without disposing of the existing content or talking to the stylesheet. I'm bloody lost and don't even know where to start looking next.
The point is... And here's a plea... If any of you do reply, I fear you will reply without the making the assumption that you're talking to someone who really hasn't got a clue what AJAX and JQuery and PHP are... I have searched forums; I don't understand them. Please bear that in mind.
I'll take a stab at updating your function a bit. I recognize that a critique of the code as it stands probably won't help you solve your problem.
var currentGallery = 'landscape';
function ChangeGallery(name) {
var imgs = document.getElementsByTagName("img") // get all the img tags on the page
for (var i = 0; i < imgs.length; i++) { // loop through them
if (imgs[i].src.indexOf(currentGallery) >= 0) { // if this img tag's src contains the current gallery
imgs[i].src = imgs[i].src.replace(currentGallery, name);
}
}
currentGallery = name;
}
As to why I've done what I've done - you're correct in that the scope of the variables - whether the whole page, or only the given function, knows about it, is mixed in your given code. However, another potential problem is that if you replace everything in the html that says 'landscape' with 'portfolio', it could potentially change non-images. This code only finds images, and then replaces the src only if it contains the given keyword.