Develop Reference

Best way to reinitialize javascript modules after ajax load

I have a bunch of JS functions/modules defined as such:
m.revealer = function(){
var els = doc.getElementsByClassName('js-reveal');
if (els.length < 1) return false;
var wh = win.innerHeight;
function checkEls(){
for (var i = 0; i < els.length; i++) {
var el = els[i],
top = el.getBoundingClientRect().top,
offset = parseFloat(el.getAttribute('data-offset')),
target;
offset = offset ? offset : 1;
target = (wh * offset);
if (top <= target && !u.hasClass(el, 'revealed')) {
u.addClass(el, 'revealed');
}
if (top > target && u.hasClass(el, 'revealed')) {
u.removeClass(el, 'revealed');
}
};
requestAnimationFrame(checkEls);
}
checkEls();
};
And they are called via:
m.installSetUp();
m.pinner();
m.installMonitor();
m.revealer();
And within those, are various things, such as event listeners, etc. Some of which are bound to window or document. They keep their variables in their own scope except for things like window, or document event listeners.
When I'm using ajax to load pages, after the page has loaded and has it's new dom I recall those functions to get them to work:
function reinit() {
doc = document;
body = doc.body;
m.navControls();
m.introVideo();
m.homeSnaps();
m.techSwitch();
m.minicartToggle();
m.installationAnims();
}
However I seem to be running in to lots of bugs where things just aren't working correctly. Things that depend on scroll are off, listeners are assigned twice, etc.
How would I best go about fixing/making sure this doesn't happen in future?
Please note: NOT using jQuery.
If more code is required, I will provide where needed.
Thanks.

Assign a Function Argument with a Loop

I have an array of list items in a piece of Javascript code. I would like to assign an onclick event handler to each one. Each handler would be the same function, but with a different input argument. Right now I have:
function contentfill(i) {
box = document.getElementById("text");
box.style.background="rgba(0,0,0,0.8)";
var content = new Array();
contentdivs = document.querySelectorAll("#contentfill>div");
box.innerHTML = contentdivs[i].innerHTML;
}
li[3].onclick = function() {contentfill(0);};
li[4].onclick = function() {contentfill(1);};
li[5].onclick = function() {contentfill(2);};
This works well enough, but I would like to achieve the same thing with a loop, for example:
for(i=3;i<=5;i++) {
j=i-3;
li[i].onclick = function() {contentfill(j);};
}
This, however, does not work. Since j seems to be defined as 2 at the end of the loop, each time I click, it only seems to call contentfill(2).

For an alternative approach, consider having each of the elements aware of what argument it should be using.
for (var i = 0; i < 3; i++) {
var el = li[i + 3];
el.dataset.contentIndex = i;
el.addEventListener('click', contentfill);
}
Then contentfill would have to extract the argument from .dataset instead of taking an argument, of course. (This is the same mechanism as jQuery's $.data.)
I tend to prefer this since (a) it doesn't generate tons of tiny wrappers, (b) it allows me to later examine and possibly change the "arguments", and (c) it lets me predefine them in the document using data- attributes. Effectively changes them from function arguments into behavior.

The value of i - 3 should be bound to the click handler function; a closure can provide this functionality:
li[i].onclick = (function(j) {
return function() {
contentfill(j);
}
)(i - 3));
Btw, it's better practice to use addEventListener or attachEvent to register click handlers.

How can I refresh a stored and snapshotted jquery selector variable

I ran yesterday in a problem with a jquery-selector I assigned to a variable and it's driving me mad.
Here is a jsfiddle with testcase:
assign the .elem to my obj var
log both lengths to the console. Result => 4
Remove #3 from the DOM
log obj to the console => the removed #3 is still there and the length is still 4.
I figured out that jquery query is snapshotted? to the variable and can't?won't? be updated
log .elem to the console.. yep Result => 3 and the #3 is gone
Now I update .elem with a new width of 300
logging obj & obj.width gives me 300.. So the snapshot has been updated ? What's interesting is that 3 of the 4 divs have the new width, but the removed #3 doesn't...
Another test: Adding a li element to the domtree and logging obj and .elem.
.elem does have the new li and obj doesn't, because it's still the old snapshot
http://jsfiddle.net/CBDUK/1/
Is there no way to update this obj with the new content?
I don't want to make a new obj, because in my application there is a lot information saved in that object, I don't want to destroy...

Yeah, it's a snapshot. Furthermore, removing an element from the page DOM tree isn't magically going to vanish all references to the element.
You can refresh it like so:
var a = $(".elem");
a = $(a.selector);
Mini-plugin:
$.fn.refresh = function() {
return $(this.selector);
};
var a = $(".elem");
a = a.refresh();
This simple solution doesn't work with complex traversals though. You are going to have to make a parser for the .selector property to refresh the snapshot for those.
The format is like:
$("body").find("div").next(".sibling").prevAll().siblings().selector
//"body div.next(.sibling).prevAll().siblings()"
In-place mini-plugin:
$.fn.refresh = function() {
var elems = $(this.selector);
this.splice(0, this.length);
this.push.apply( this, elems );
return this;
};
var a = $(".elem");
a.refresh() //No assignment necessary

I also liked #Esailija solution, but seems that this.selector has some bugs with filter.
So I modified to my needs, maybe it will be useful to someone
This was for jQuery 1.7.2 didn`t test refresh on filtered snapshots on higher versions
$.fn.refresh = function() { // refresh seletor
var m = this.selector.match(/\.filter\([.\S+\d?(\,\s2)]*\)/); // catch filter string
var elems = null;
if (m != null) { // if no filter, then do the evarage workflow
var filter = m[0].match(/\([.\S+\d?(\,\s2)]*\)/)[0].replace(/[\(\)']+/g,'');
this.selector = this.selector.replace(m[0],''); // remove filter from selector
elems = $(this.selector).filter(filter); // enable filter for it
} else {
elems = $(this.selector);
}
this.splice(0, this.length);
this.push.apply( this, elems );
return this;
};
Code is not so beautiful, but it worked for my filtered selectors.

Clean and generic solution worked properly with jQuery 3.4.1:
My solution is to do the following:
Intercept the selector at the time of jQuery object initialization and in the same time maintain all other jQuery functionalities transparently all this using inheritance
Build refresh plugin that make use of the new "selector" property we added during initialization
Definition:
$ = (function (originalJQuery)
{
return (function ()
{
var newJQuery = originalJQuery.apply(this, arguments);
newJQuery.selector = arguments.length > 0 ? arguments[0] : null;
return newJQuery;
});
})($);
$.fn = $.prototype = jQuery.fn;
$.fn.refresh = function ()
{
if (this.selector != null && (typeof this.selector === 'string' || this.selector instanceof String))
{
var elems = $(this.selector);
this.splice(0, this.length);
this.push.apply(this, elems);
}
return this;
};
Usage:
var myAnchors = $('p > a');
//Manipulate your DOM and make changes to be captured by the refresh plugin....
myAnchors.refresh();
//Now, myAnchors variable will hold a fresh snapshot
Note:
As optimization, object selectors don't need refresh as they are pass by reference by nature so, in refresh plugin, we only refresh if the selector is a string selector not object selector for clarification, consider the following code:
// Define a plain object
var foo = { foo: "bar", hello: "world" };
// Pass it to the jQuery function
var $foo = $( foo );
// Test accessing property values
var test1 = $foo.prop( "foo" ); // bar
// Change the original object
foo.foo = "koko";
// Test updated property value
var test2 = $foo.prop( "foo" ); // koko

Jquery .selector is deprecated, it's better to remeber string with selector value to some variable at the moment when you assign
function someModule($selector, selectorText) {
var $moduleSelector = $selector;
var moduleSelectorText = selectorText;
var onSelectorRefresh = function() {
$moduleSelector = $(moduleSelectorText);
}
}
https://api.jquery.com/selector/

You can also return the JQuery selector in a function, and save this function into the variable. Your code will look a bit different but it works. Every time when you execute the function, your jquery selector will search the DOM again.
In this example I used an arrow function without brackets which will return whatever is next to arrow. In this case it will return the JQuery collection.
const $mySelector = () => $('.selector');
console.log($mySelector().last().text());
$('.parent').append('<li class="selector">4</li>')
console.log($mySelector().last().text()); //RETURNS 4 not 3
<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>
<ul class="parent">
<li class="selector">1</li>
<li class="selector">2</li>
<li class="selector">3</li>
</ul>

If you use remove() it will remove only a part of the DOM but not all the children or related, instead if you use empty() on the element the problem is gone.
E.G.:
$('#parent .child).find('#foo').empty();
Maybe it can be useful to someone!

JavaScript - Loop over all a tags, add an onclick to each one

I've got a list of links that point to images, and a js function that takes a URL (of an image) and puts that image on the page when the function is called.
I was originally adding an inline onlick="showPic(this.getAttribute('href'))" to each a, but I want to separate out the inline js. Here's my func for adding an onclick to each a tag when the page loads:
function prepareLinks(){
var links = document.getElementsByTagName('a');
for(var i=0; i<links.length; i++){
var thisLink = links[i];
var source = thisLink.getAttribute('href');
if(thisLink.getAttribute('class') == 'imgLink'){
thisLink.onclick = function(){
showPic(source);
return false;
}
}
}
}
function showPic(source){
var placeholder = document.getElementById('placeholder');
placeholder.setAttribute('src',source);
}
window.onload = prepareLinks();
...but every time showPic is called, the source var is the href of the last image. How can I make each link have the correct onclick?

JavaScript doesn't have block scope, so the closed variable ends up being whatever was last assigned to it. You can fix this by wrapping it in another closure:
function prepareLinks() {
var links = document.getElementsByTagName('a');
for(var i = 0; i < links.length; i++) {
var thisLink = links[i];
var source = thisLink.getAttribute('href');
if(thisLink.getAttribute('class') == 'imgLink') {
thisLink.onclick = (function(source) {
return function() {
showPic(source);
return false;
};
})(source);
}
}
}
Of course, you can make this one simpler and use this:
function prepareLinks() {
var links = document.getElementsByTagName('a');
for(var i = 0; i < links.length; i++) {
var thisLink = links[i];
if(thisLink.getAttribute('class') == 'imgLink') {
thisLink.onclick = function() {
showPic(this.href);
return false;
};
}
}
}
I believe this either breaks compatibility with IE5 or IE6, but hopefully you don't care about either of those =)

Minitech's answer should fix your problem, which is that the source variable is shared by all your onclick handlers
The way you're doing it is very wasteful, there's no need to set a separate handler for each link. Also, it won't work if any links are added dynamically. Event delegation is the way to go.
function interceptLinks() {
// Bad way to set onclick (use a library)
document.onclick = function() {
if (this.tagName.toUpperCase() != 'A' ) {
return;
}
// Bad way to check if it contains a class (use a library)
if (this.getAttribute('class') == 'imgLink') {
showPic(this.getAttribute('href'));
return false;
}
}
}

This is the age-old problem of event handlers inside of a loop that access an outer variable.
Your source variable is pulled off the scope chain at the time of the click event, and by then, it's been set to the last href attribute due to the iteration being finished.
You need to break the closure by doing one of two things.
The easiest but not supported by many browsers is to use let which lets you use block scope.
let source = thisLink.getAttribute('href');
jsFiddle. It worked in Firefox, but not Chrome.
In 2038, when we're dealing with the year 2038 problem and all browsers have implemented ES6, this will be the standard way to fix this problem.
A more difficult to understand and implement method that is compatible with all browsers is to break the closure with a pattern such as...
thisLink.onclick = (function(src) {
return function(){
showPic(src);
return false;
}
})(source);
jsFiddle.

Thanks for all the replies. Turns out I had diagnosed the problem incorrectly, sorry. Actually using a new var and annon. function to add an onclick on each loop iteration works (the passed href is correct). It was not working because I was getting at the a-tags by the "imgLink" class which I had removed from the HTML when I removed the inline onclick handlers (I get them with an ID on a parent now). Also I needed to use "return !showPic(this.href);" to stop the link being followed normally when clicked.
Working code:
function showPic(source){
var placeholder = document.getElementById('placeholder');
placeholder.setAttribute('src',source);
return true;
}
function prepareLinks() {
if(!document.getElementById('imgLinks')){ return false; };
var galLinks = document.getElementById('imgLinks');
var links = galLinks.getElementsByTagName('a');
for(var i=0; i<links.length; i++) {
var thisLink = links[i];
thisLink.onclick = function() {
return !showPic(this.href);
};
}
}
window.onload = function(){
prepareLinks();
}

Transfer HTML elements from one list to another with JavaScript

I have a problem with the following JavaScript function. I have two UL and I need that when the user clicks on a LI, this element transfers to the other UL.
I've managed to move them onClick from on list to the other, the problem appears when I try to move again a LI that was previously in the other UL, when that happens it just doesn't work...
function testList() {
usersA = document.getElementById("users-a");
usersB = document.getElementById("users-b");
for (var i=0; i < usersA.getElementsByTagName("li").length; i++) {
usersA.getElementsByTagName("li")[i].onclick = function() {
transfer = this.cloneNode(true);
usersB.appendChild(transfer);
usersA.removeChild(this);
return false;
}
}
for (var i=0; i < usersB.getElementsByTagName("li").length; i++) {
usersB.getElementsByTagName("li")[i].onclick = function() {
transfer = this.cloneNode(true);
usersA.appendChild(transfer);
usersB.removeChild(this);
return false;
}
}
}
I know that my logic sucks but it's all I could come up with. Any ideas why it works the first time I transfer a LI but when I try to move back to its original UL it doesn't work?

You're not "moving" elements, you're creating a copy and deleting the original. Although this seems like a "move" from the user's point of view the new elements that you create do not have click handlers assigned. From MDN: "Cloning a node copies all of its attributes and their values but does not copy event listeners."
According to MDN, .appendChild() will remove the child from its current parent so you shouldn't need the two-step clone/remove that you are currently doing. I haven't tested it, but perhaps using just .appendChild() it will keep the handlers? If so you need to remove that handler and assign a new one to allow for which list it now belongs to.
Or, rewrite your handlers so that they check which list is the current parent (have a look at .parentNode) and move to the other list as appropriate.
Bearing in mind that click events "bubble up" starting from the target/source element and up through the parent heirarchy you're probably better off setting your click handlers on the parent <ul> elements and then testing which <li> was clicked. That way you don't have to worry about setting new click handlers on new child <li> elements.
function testList() {
var usersA = document.getElementById("users-a"),
usersB = document.getElementById("users-b");
usersA.onclick = function(e) {
// allow for the IE and non-IE way of handling the event object
if (!e) e = window.event;
var el = e.target || e.srcElement;
if (el.tagName === "li") {
usersB.appendChild(el);
}
}
usersB.onclick = function(e) {
// allow for the IE and non-IE way of handling the event object
if (!e) e = window.event;
var el = e.target || e.srcElement;
if (el.tagName === "li") {
usersA.appendChild(el);
}
}
}
Also, if you're using .getElementsByTagName() call it once in the loop initialisation and assign the result to a variable, then use the variable - don't keep calling the function again and again to test the length, or to access individual elements inside your loop:
for (var i=0, lis = usersA.getElementsByTagName("li"); i < lis.length; i++) {
lis[i].onclick = function() {
// etc
}
}

The problem is that even after you've moved an element from list A to list B, it still keeps its old onclick handler, which still says "remove me from list A and add me to list B". You need to change its onclick handler to say "remove me from list B and add me to list A". Here's one way to fix that:
var usersA = document.getElementById("users-a");
var usersB = document.getElementById("users-b");
var onclickA;
var onclickB = function() {
usersA.appendChild(this);
this.onclick = onclickA;
return false;
};
onclickA = function() {
usersB.appendChild(this);
this.onclick = onclickB;
return false;
};
for (var i=0; i < usersA.getElementsByTagName("li").length; i++)
usersA.getElementsByTagName("li")[i].onclick = onclickA;
for (var i=0; i < usersB.getElementsByTagName("li").length; i++)
usersB.getElementsByTagName("li")[i].onclick = onclickB;
(I also got rid of the cloneNode stuff, for exactly the reasons that nnnnnn gives.)