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Javascript before and after events for window resize

onresize can be used for knowing window has been resized. Is there any similar notification/event before window resizes.
I want to set will-change on some elements before window resize starts and subsequently remove that after window has resized.

It seems there are no direct solutions but you can achieve both start|end events with some workaround using window.addEventListener("resize",yourFunction); and some global variables (it is a workaround, it is not perfect).
//Accesible variables
var atStart = true;
var timer;
function yourFunction(){
return ()=>{
if(atStart){
console.log("START");
//Some code to be executed once at start
atStart = false;
}
console.log("WHILE");
//Some code to be executed while resizing
if (timer) clearTimeout(timer);
timer= setTimeout(atEnd, 500);
}
}
function atEnd(){
//Some code to be executed at the end of resizing
//..well some 500ms after the end of resizing
console.log("END")
atStart = true;
}
window.addEventListener("resize",yourFunction());
Hope it helps someone.

There are no events that fire before resize. Only during resize. Most solutions to do something on rezise use setTimeout to check when a certain amount of time passed since the last resize event. So I guess you're out of luck.

Fire jQuery when breakpoint is reached

I have a responsive design with multiple breakpoints. Some of the block dimensions in the content are calculated with jQuery. When the viewport changes these dimensions change thus the calculation should be run. How can I fire these events when the dimension of the reference element changes? The reference element changes when a breakpoint is crossed.
I've looked at the "orientationchange" event but it's not having the results I need.

You provide very little specifics and no code so all we can do is answer very generally.
Usually, you install a .resize() event handler and on every resize of the containing window, you check to see if the resulting dimensions have changed such that you need to recalculate and modify the layout.
$(window).resize(function(e) {
// check dimensions here to decide if layout needs to be adjusted
});
jQuery mobile supports the orientationchange event like this which also gives you e.orientation as "portrait" or "landscape":
$(window).on( "orientationchange", function(e) {
// check dimensions here to decide if layout needs to be adjusted
});
There are no DOM events for watching a size change on a specific element in the page other than a window object. Instead, you have to watch whatever other events might cause a given element to get resized which might be a resize of the window, an orientation change or some other action in the page that modifies the page (a button press or click on something, for example). Then, when those other events fire and get processed, you can then check the size of your target element and see if it changed.
Here's a jQuery plugin that debounces the resize event so it only tells you about a resize when the size has stopped changing:
(function($) {
var uniqueCntr = 0;
$.fn.resized = function (waitTime, fn) {
if (typeof waitTime === "function") {
fn = waitTime;
waitTime = 250;
}
var tag = "resizeTimer" + uniqueCntr++;
this.resize(function () {
var self = $(this);
var timer = self.data(tag);
if (timer) {
clearTimeout(timer);
}
timer = setTimeout(function () {
self.removeData(tag);
fn.call(self[0]);
}, waitTime);
self.data(tag, timer);
});
}
})(jQuery);
Working demo: https://jsfiddle.net/jfriend00/k415qunp/
Sample usage:
$(window).resized(function() {
// put code here to act when window stopped getting resized
});

This page might help you. They talk about JS execution based on breakpoints and doing it with cross-browser support. Basically you'll be using a hidden pseudo element using the "content" property of .myClass:after.

Fade in or fade out based on scroll

$(document).scroll(function () {
var y = $(this).scrollTop();
if (y > 397) {
$('#aboutNav.fixed').fadeIn(500);
} else {
$('#aboutNav.fixed').hide();
}
});
As you can tell, this shows a fixed navigation. The CSS is fine, the positioning is great. However I want the navigation to become visible above 397px which it does fine.
However I want the navigation to fade in when I start scrolling:
.fadeIn(500);
When the user starts stops to look at content or whatever, I want the element to fade out
.delay(3000).fadeOut(350);
I believe this is something that can be done by doing an if statement within the first if statement. However a script to check if the user is scrolling and the working script above seem to collide.
Ideas, anyone?

If I understand you correctly. You want the nav to fade in if its above 397px and only when its scrolling... So this function will do that. If I misunderstood your question please clarify in the comments
$(window).scroll(function() {
clearTimeout($.data(this, 'scrollTimer'));//Lets the timer know were scrolling
//Hide/Show nav based on location
var y = $(this).scrollTop();
if (y > 397) {
$('#aboutNav.fixed').fadeIn(500);
} else {
$('#aboutNav.fixed').hide();
}
//TimeOut function that is only hit if we havent scrolled for 3 Seconds
//In here is where you fade out the nav
$.data(this, 'scrollTimer', setTimeout(function() {
$('#aboutNav.fixed').fadeOut();
console.log("Haven't scrolled in 3s!");
}, 3000));
});
JAN 23 UPDATE based on your comment
You can add this to you $(document).ready() function
$("#elementID").hover(function(){
//show here (mouse over)
$("#elementToShow").show();
},function(){
//Start timeout here, (mouse out)
setTimeout(function() {
$("#elementToHide").hide();
}, 3000);
}

Expanding on what Kierchon's answer a bit:
Since there's no real way to tell when the user is done scrolling (i.e. no event for 'finished scrolling') you'll have to use a event-delaying method called debouncing.
Debouncing is basically setting a timeout to run some code (a function) in the future, and if the event calling the debounced function get called again, you clear and reset the timeout, doing this repeatedly until the event finally stops being called. This method is to prevent events that fire repeatedly (such as scroll and resize) to only execute things after the final event fires and your delayed (debounced) code finally executes.
Here is a nice article on use of debouncing methods in JS.
As long as I understand what you need (which I think I do) - Here's a JSBin with some working code

jQuery Click event triggers more times on every window resize

People!
This is the first time I come here to ask something, so far, always when I had a problem, I could find a good answer here. So, in first place, thanks for this amazing community!
Now let's go to the problem:
I'm doing a responsive menu that check the window.resize event and, when it fits the minimum browser width, a click function for a button is allowed. If the browser width is greater, then the click function is unbound. I need to do this because the same element that is the button on the mobile version, is a visual element on the desktop version.
The problem is that, with the code that I have now, when the page is loaded, the click function works fine. But, if I resize the browser and click on the element again, it triggers more than once the state, sometimes leaving the impression that the function isn't triggered. And, if I resize the browser again, it triggers the click function more than the last time I clicked. Really annoying.
To help understand what is happening, I've made a simple example. Here's is the simple code (just to check the click function issue):
HTML:
<ul>
<li><span class="sub-toggle">Testing 01</span></li>
<li><span class="sub-toggle">Testing 02</span></li>
<li><span class="sub-toggle">Testing 03</span></li>
</ul>
CSS:
.sub-toggle{
display:block;
padding: 20px;
}
.sub-toggle.active{
background-color: #ffcc00;
color: #fff;
}
Javascript (jQuery):
jQuery(function($){
var i = 1;
// check if browser size is compatible with click event
onResize = function() {
// if browser size is ok, do the click function
if($(window).width() <= 480){
// click function
$('.sub-toggle').click(function(){
alert('click');
if($(this).hasClass('active')){
alert('active');
$(this).removeClass('active');
} else {
$(this).addClass('active');
}
});
} else{
// if browser size is greater than expected, unbind the click function
$('.sub-toggle').removeClass('active').unbind('click');
}
// just checking how many times the resize function is triggered
console.log('resize: '+ i);
i++;
}
$(document).ready(onResize);
var timer;
$(window).bind('resize', function(){
timer && clearTimeout(timer);
timer = setTimeout(onResize, 500);
});
});
(Edited to remove some unnecessary code)
If you want to see it in action, I've made a Fiddle (try resize the output frame to see it working): http://jsfiddle.net/C7ppv/1/
Maybe I've missing something really stupid, since I don't have a huge knowledge in JavaScript. But what I want to do is just trigger the click event once, even if multiple resizes.
I hope I could explain well my problem. I've searched and didn't found a solution for this issue (or maybe I just didn't know really well what to look for).
Any help would be appreciated!

Your code currently binds a new click events every time the method onResize is called and the window width is less than or equal to 480px.
Simply unbind any existing click events on the .sub-toggle element before binding a new one.
$('.sub-toggle').unbind('click').click(function() {
...
});
DEMO

The resize event is triggered multiple times during resizing, and each time you're binding a new click handler. My suggestion: bind only once, from outside the resize handler, and set a flag while resizing to let the click handler know if it should do something or not.
Then you won't even need to defer the handling of resize with setTimeout as you're doing.
DEMO
jQuery(function($){
var i = 1;
// flag to allow clicking
var clickAllowed = true;
// click function
$('.sub-toggle').click(function(){
if(clickAllowed) {
alert('click');
if($(this).hasClass('active')){
alert('active');
$(this).removeClass('active');
} else {
$(this).addClass('active');
}
}
});
// check if browser size is compatible with click event
onResize = function() {
//if browser size is ok, do the click function
if($(window).width() <= 480){
clickAllowed = true;
}
else{
// if browser size is greater than expected, disallow clicking
clickAllowed = false;
}
// just checking how many times the resize function is triggered
console.log('resize: '+ i);
i++;
}
$(document).ready(onResize);
var timer;
$(window).bind('resize', onResize);
});

Move $('.sub-toggle').click(function(){...} outside the onResize event handler and move if($(window).width() <= 480){...} into the click handler.

Javascript: do an action after user is done scrolling

I'm trying to figure out a way to do this. I have a list of boxes, each about 150px high. I am using javascript (and jquery) and want that, after a user scrolls down a page, the page will auto scroll so that the boxes line up with the rest of the page (that is to say, if the user scrolls and the y position of the page is not divisible by 150, it will scroll to that nearest point).
Now, I at the moment, I know I can activate an event using the .scroll() jquery event, and I can make it move to a certain point using .scrollTop(). But every pixel the user moves the scroll bar activates the whole function. So is there a way to delay the function from firing until the user hasn't scrolled, and if they should begin to scroll again, the function will halt?

As you are already using jQuery, have a look at Ben Alman's doTimeout plugin which already handles the debouncing of methods (which is what you are after).
Example shamelessly stolen from his website:
$(window).scroll(function(){
$.doTimeout( 'scroll', 250, function(){
// do something computationally expensive
});
});

This is basically the same as Šime Vidas' answer, but less complex:
var scrollTimeout = null;
$(window).scroll(function(){
if (scrollTimeout) clearTimeout(scrollTimeout);
scrollTimeout = setTimeout(function(){yourFunctionGoesHere()},500);
});
500 is the delay. Should be ok for mouse scroll.

Sure, in the event handler for the scroll event, fire off a setTimeout for 100 or 200 milliseconds later. Have that setTimeout function you set inside of the scroll event handler do the positioning logic you mention above. Also have the scroll event handler clear any timeouts set by itself. This way, the last time the scroll event fires, the setTimeout function will get to complete as the scroll event has not cleared it.

The code:
var scrollTimeout = null;
var scrollendDelay = 500; // ms
$(window).scroll(function() {
if ( scrollTimeout === null ) {
scrollbeginHandler();
} else {
clearTimeout( scrollTimeout );
}
scrollTimeout = setTimeout( scrollendHandler, scrollendDelay );
});
function scrollbeginHandler() {
// this code executes on "scrollbegin"
document.body.style.backgroundColor = "yellow";
}
function scrollendHandler() {
// this code executes on "scrollend"
document.body.style.backgroundColor = "gray";
scrollTimeout = null;
}

This would be a scenario, where vanilla JavaScript would be useful.
var yourFunction = function(){
// do something computationally expensive
}
$(window).scroll(function(){
yfTime=setTimeout("yourFunction()",250);
});