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JavaScript(Canvas): How to update the pointer's position inside the animation frame and NOT inside the event listener? [duplicate]

Is it possible to get the mouse position with JavaScript after page loads without any mouse movement event (without moving the mouse)?

Real answer: No, it's not possible.
OK, I have just thought of a way. Overlay your page with a div that covers the whole document. Inside that, create (say) 2,000 x 2,000 <a> elements (so that the :hover pseudo-class will work in IE 6, see), each 1 pixel in size. Create a CSS :hover rule for those <a> elements that changes a property (let's say font-family). In your load handler, cycle through each of the 4 million <a> elements, checking currentStyle / getComputedStyle() until you find the one with the hover font. Extrapolate back from this element to get the co-ordinates within the document.
N.B. DON'T DO THIS.

Edit 2020: This does not work any more. It seems so, that the browser vendors patched this out. Because the most browsers rely on chromium, it might be in its core.
Old answer:
You can also hook mouseenter (this event is fired after page reload, when the mousecursor is inside the page). Extending Corrupted's code should do the trick:
var x = null;
var y = null;
document.addEventListener('mousemove', onMouseUpdate, false);
document.addEventListener('mouseenter', onMouseUpdate, false);
function onMouseUpdate(e) {
x = e.pageX;
y = e.pageY;
console.log(x, y);
}
function getMouseX() {
return x;
}
function getMouseY() {
return y;
}
You can also set x and y to null on mouseleave-event. So you can check if the user is on your page with it's cursor.

What you can do is create variables for the x and y coordinates of your cursor, update them whenever the mouse moves and call a function on an interval to do what you need with the stored position.
The downside to this of course is that at least one initial movement of the mouse is required to have it work. As long as the cursor updates its position at least once, we are able to find its position regardless of whether it moves again.
var cursor_x = -1;
var cursor_y = -1;
document.onmousemove = function(event)
{
cursor_x = event.pageX;
cursor_y = event.pageY;
}
setInterval(check_cursor, 1000);
function check_cursor(){console.log('Cursor at: '+cursor_x+', '+cursor_y);}
The preceding code updates once a second with a message of where your cursor is.

#Tim Down's answer is not performant if you render 2,000 x 2,000 <a> elements:
OK, I have just thought of a way. Overlay your page with a div that
covers the whole document. Inside that, create (say) 2,000 x 2,000
elements (so that the :hover pseudo-class will work in IE 6, see),
each 1 pixel in size. Create a CSS :hover rule for those elements
that changes a property (let's say font-family). In your load handler,
cycle through each of the 4 million elements, checking
currentStyle / getComputedStyle() until you find the one with the
hover font. Extrapolate back from this element to get the co-ordinates
within the document.
N.B. DON'T DO THIS.
But you don't have to render 4 million elements at once, instead use binary search. Just use 4 <a> elements instead:
Step 1: Consider the whole screen as the starting search area
Step 2: Split the search area into 2 x 2 = 4 rectangle <a> elements
Step 3: Using the getComputedStyle() function determine in which rectangle mouse hovers
Step 4: Reduce the search area to that rectangle and repeat from step 2.
This way you would need to repeat these steps max 11 times, considering your screen is not wider than 2048px.
So you will generate max 11 x 4 = 44 <a> elements.
If you don't need to determine the mouse position exactly to a pixel, but say 10px precision is OK. You would repeat the steps at most 8 times, so you would need to draw max 8 x 4 = 32 <a> elements.
Also generating and then destroying the <a> elements is not performat as DOM is generally slow. Instead, you can just reuse the initial 4 <a> elements and just adjust their top, left, width and height as you loop through steps.
Now, creating 4 <a> is an overkill as well. Instead, you can reuse the same one <a> element for when testing for getComputedStyle() in each rectangle. So, instead of splitting the search area into 2 x 2 <a> elements just reuse a single <a> element by moving it with top and left style properties.
So, all you need is a single <a> element change its width and height max 11 times, and change its top and left max 44 times and you will have the exact mouse position.

You could try something similar to what Tim Down suggested - but instead of having elements for each pixel on the screen, create just 2-4 elements (boxes), and change their location, width, height dynamically to divide the yet possible locations on screen by 2-4 recursively, thus finding the mouse real location quickly.
For example - first elements take right and left half of screen, afterwards the upper and lower half. By now we already know in which quarter of screen the mouse is located, are able to repeat - discover which quarter of this space...

Here's my solution. It exports window.currentMouseX and window.currentMouseY properties you can use anywhere. It uses the position of a hovered element (if any) initially and afterwards listens to mouse movements to set the correct values.
(function () {
window.currentMouseX = 0;
window.currentMouseY = 0;
// Guess the initial mouse position approximately if possible:
var hoveredElement = document.querySelectorAll(':hover');
hoveredElement = hoveredElement[hoveredElement.length - 1]; // Get the most specific hovered element
if (hoveredElement != null) {
var rect = hoveredElement.getBoundingClientRect();
// Set the values from hovered element's position
window.currentMouseX = window.scrollX + rect.x;
window.currentMouseY = window.scrollY + rect.y;
}
// Listen for mouse movements to set the correct values
window.addEventListener('mousemove', function (e) {
window.currentMouseX = e.pageX;
window.currentMouseY = e.pageY;
}, /*useCapture=*/true);
}())
Composr CMS Source: https://github.com/ocproducts/composr/commit/a851c19f925be20bc16bfe016be42924989f262e#diff-b162dc9c35a97618a96748639ff41251R1202

The most simple solution but not 100% accurate
$(':hover').last().offset()
Result: {top: 148, left: 62.5}
The result depend on the nearest element size and return undefined when user switched the tab

Yes, It's possible.
If you add "mouseover" event to the document it will fire instantly and you can get the mouse position, of course if mouse pointer was over the document.
document.addEventListener('mouseover', setInitialMousePos, false);
function setInitialMousePos( event ) {
console.log( event.clientX, event.clientY);
document.removeEventListener('mouseover', setInitialMousePos, false);
}
Previously it was possible to read mouse position through window.event but it's deprecated now.

var x = 0;
var y = 0;
document.addEventListener('mousemove', onMouseMove, false)
function onMouseMove(e){
x = e.clientX;
y = e.clientY;
}
function getMouseX() {
return x;
}
function getMouseY() {
return y;
}

I implemented a horizontal/vertical search, (first make a div full of vertical line links arranged horizontally, then make a div full of horizontal line links arranged vertically, and simply see which one has the hover state) like Tim Down's idea above, and it works pretty fast. Sadly, does not work on Chrome 32 on KDE.
jsfiddle.net/5XzeE/4/

You do not have to move the mouse to get the cursor's location. The location is also reported on events other than mousemove. Here's a click-event as an example:
document.body.addEventListener('click',function(e)
{
console.log("cursor-location: " + e.clientX + ',' + e.clientY);
});

Riffing on #SuperNova's answer, here's an approach using ES6 classes that keeps the context for this correct in your callback:
class Mouse {
constructor() {
this.x = 0;
this.y = 0;
this.callbacks = {
mouseenter: [],
mousemove: [],
};
}
get xPos() {
return this.x;
}
get yPos() {
return this.y;
}
get position() {
return `${this.x},${this.y}`;
}
addListener(type, callback) {
document.addEventListener(type, this); // Pass `this` as the second arg to keep the context correct
this.callbacks[type].push(callback);
}
// `handleEvent` is part of the browser's `EventListener` API.
// https://developer.mozilla.org/en-US/docs/Web/API/EventListener/handleEvent
handleEvent(event) {
const isMousemove = event.type === 'mousemove';
const isMouseenter = event.type === 'mouseenter';
if (isMousemove || isMouseenter) {
this.x = event.pageX;
this.y = event.pageY;
}
this.callbacks[event.type].forEach((callback) => {
callback();
});
}
}
const mouse = new Mouse();
mouse.addListener('mouseenter', () => console.log('mouseenter', mouse.position));
mouse.addListener('mousemove', () => console.log('mousemove A', mouse.position));
mouse.addListener('mousemove', () => console.log('mousemove B', mouse.position));

Not mouse position, but, if you're looking for current cursor postion (for use cases like getting last typed character etc) then, below snippet works fine.
This will give you the cursor index related to text content.
window.getSelection().getRangeAt(0).startOffset

I envision that maybe you have a parent page with a timer and after a certain amount of time or a task is completed, you forward the user to a new page. Now you want the cursor position, and because they are waiting, they aren't necessarily touching the mouse. So track the mouse on the parent page using standard events and pass the last value to the new page in a get or a post variable.
You can use JHarding's code on your parent page so that the latest position is always available in a global variable:
var cursorX;
var cursorY;
document.onmousemove = function(e){
cursorX = e.pageX;
cursorY = e.pageY;
}
This won't help users that navigate to this page by means other than your parent page.

I think i may have a reasonable solution with out counting divs and pixels..lol
Simply use animation frame or a time interval of a function. you will still need a mouse event one time though just to initiate, but technically you position this where ever you like.
Essentially we are tracking a dummy div at all times with out mouse movement.
// create a div(#mydiv) 1px by 1px set opacity to 0 & position:absolute;
Below is the logic..
var x,y;
$('body').mousemove(function( e ) {
var x = e.clientX - (window.innerWidth / 2);
var y = e.clientY - (window.innerHeight / 2);
}
function looping (){
/* track my div position 60 x 60 seconds!
with out the mouse after initiation you can still track the dummy div.x & y
mouse doesn't need to move.*/
$('#mydiv').x = x; // css transform x and y to follow
$('#mydiv)'.y = y;
console.log(#mydiv.x etc)
requestAnimationFrame( looping , frame speed here);
}

Auto-Update Javascript

I want a div to move when the mouse is within x distance from it.
$(document).mousemove(function(e) {
mX = e.pageX;
mY = e.pageY;
distance = calculateDistance(element, mX, mY);
if (distance<100) {
$(element).css("left", moveAcc + "px");
moveAcc = moveAcc + 1;
}
});
JSFiddle - You have to select jquery 1.11.0 library
But because the condition is inside the mousemove function, it can only move the element when the mouse is being moved too, as opposed to moving when mouse is within x distance.
For this I need sort of an update thingy, something to check if conditions are met every frame.
Example, in Pascal for my projects I'd put the whole code in between the repeat until ()
In ActionScript there's addEventListener(Event.ENTER_FRAME, function);
What can I use in Javascript? What other ways would you come up with? - I did found this Javascript Version of AS3 enterframe event but it is 4 years old, migh be different now.
Is it ok to put the code inside setInterval function?

You're looking for the requestAnimationFrame method.
What it does ? It'll execute the method passed on it call before the next frame get rendered. But beware, not all browsers support it, you can use a polyfill for it or just an setInterval
Example:
function checkDistance () {
\\ Do your job here
window.requestAnimationFrame(checkDistance);
}
window.requestAnimationFrame(checkDistance);
More info:
https://developer.mozilla.org/en-US/docs/Web/API/window/requestAnimationFrame

You have two ways to do that:
Add an event listener on the document object and measure the element positions and the mouse positions, then check if the current mouse position is between those positions. (This way not suggested if you have just one element)
Add an event listener on the element directly and check if the current mouse position is exactly the same position you want.
If you have a well written mouse event listener, then you don't need to update the function using interval.

I would try declaring your mouse X and Y variables outside the mousemove method, that way even when your mouse stops moving, the last position (current really) is still accessible..
var mX;
var mY;
$(document).mousemove( function(e) {
mX = e.pageX;
mY = e.pageY;
});
Then, you can have a second method on an interval that can check against the values in those variables, and move the box accordingly..
setInterval(function(){
// Code to calculate distance etc.
distance = calculateDistance(element, mX, mY);
if (distance<100) {
$(element).css("left", moveAcc + "px");
moveAcc = moveAcc + 1;
}
},100); // Whatever interval you see fit instead of 100ms

Whether element is behind inner nested scroll

How to detect if an element inside a scrollable block is visible to user (i.e. is in the visible area of the scrollable parent)?
Is there a universal solution, not involving iterating over all parent nodes that have scroll?
P.S. One idea I had was getElementAtPoint, however it gives me headaches when I need to determine if at least 50% of the element is visible. So ideally the solution must involve collision detection between two rectangles: the element rectangle and the window.
P.P.S. Another idea I've come up with is to use scrollIntoView on the element in question, determine the difference in its position, and then scroll it back to original position. It appears scrollIntoView always does the right thing – scrolls both window and the inner scrollable blocks!

I'm afraid this can't be done without iterating, and even less cross-browser, with some simple code.
Here's an example, how this can be done in IE. Unfortenately other browsers seem to return different values from body/html.getBoundingClientRect(). Also margins are treated differently, (IE ignores, others take them account).
getVisibilityPercent = function () {
var target = document.getElementById('target'),
height = target.offsetHeight,
parent = target.parentElement,
targetRect = target.getBoundingClientRect(),
tLim, bLim,
percent = 1;
while (parent) {
parentRect = parent.getBoundingClientRect();
tLim = Math.max(targetRect.top, parentRect.top);
bLim = Math.min(targetRect.bottom, parentRect.bottom);
percent *= (bLim - tLim) / height;
percent = (percent < 0) ? 0 : percent;
parent = parent.parentElement;
}
return +((percent * 100).toFixed(2));
};

Function to get position of an element relative to the top-most window

This has probably been asked already, but I was not able to find any fix for what I am trying to do.
I am trying to find the magical combination of properties on the event object, along with scrolling and other offsets, to give me the position of an element relative to the top-most window that may or may not exist within an iframe. I am doing this in an attempt to fade in a small (absolutely positioned) image to the right of the element that is being moused over.
I am trying to get the position inside of a jQuery hover event. I have tried different combinations of the following properties:
$(element).position()
$(element).offset()
$(element).scrollTop()
$(element).scrollLeft();
$(document).scrollTop();
$(document).scrollLeft();
event.clientX
event.clientY
event.pageX
event.pageY
Does anyone have a function or equation that can give these numbers?

The easiest way in modern browsers is document.querySelector('.foo').getBoundingClientRect() which return's and object containing the properties top and left, which are the offsets of the element relative to the viewport.
The above method works in IE >= 5 with a couple of easy hacks see http://ejohn.org/blog/getboundingclientrect-is-awesome/
Alternatively you can use the jQuery.offset() method, if you have jQuery on the page. Which will return the elements offset consistently cross browser.
Getting the offset of said element from an <iframe> can be a bit trickier depending on where your trying to get the position from i.e. is the script running on the same page as the element which might be in an <iframe>, or in the root page with the element in the <iframe>
If you are in the first case, you don't need to do anything as long as your element is being repositioned somewhere inside the <iframe> as you already have the correct offset.
if you are outside the <iframe> you need to take the iframe.getBoundClientRect() offsets into consideration, as the element.getBoundingClientRect() is relative to it's own viewport (the <iframe>)

I've managed to finagle some code that worked for this situation. Hope this helps someone in the future:
var timeoutID;
$(element).hover(function () {
// cancel any pending fades
window.clearTimeout(timeoutID);
var offset = {
left: 0,
top: 0
};
if (top !== self) {
offset = top.$('#divContainingIframes').offset();
}
var that = $(this);
var elementPosition = that.position();
var xCoord = offset.left + // distance between screen and iframe
elementPosition.left + // distance between iframe and element
that.width() + // width of the element
5; // 5 pixel padding
var yCoord = offset.top + // distance between screen and iframe
elementPosition.top; // distance between iframe and element
// call the show function with xCoord and yCoord
}, function () {
// don't fade immediately, wait a half second
timeoutID = setTimeout(function () {
// call some hide function
}, 500);
});

unit of increment in scrollable areas / divs in javascript?

in javascript can I make sure that my large div scroll vertically
only in chunks of (let's say) 16 pixels
In java, those are called 'units of increment'.
I can't find anything similar in javascript:
I want to ensure that a certain area (div) when partially scrolled is always a multiple of 16 the view.
That allows me to do tricks with background images and others.
thanks

var lastScroll = 0;
$('div').scroll(function(){
var el = $(this),
scroll = el.scrollTop(),
round = lastScroll < scroll ? Math.ceil : Math.floor;
lastScroll = round(scroll/16) * 16;
el.scrollTop(lastScroll);
});
http://jsfiddle.net/m9DQR/2/
Ensures scrolls are done in multiples of 16 pixels. You can easily extend this to be a plugin that allows for a variable amount (not a fixed, magical 16).

Yes, this is possible, but it will require using javascript to capture the scroll event and then manipulate it. This script (sorry jQuery is what I had) and overrides the scroll event. It then replaces it with the exact same scroll distance. You could perform your own math to adjust the value of scrollTo. We have to check both mousewheel and DOMMouseScroll events because the first is not supported by FF. This doesn't seem to apply in your case, but a user may have the number of lines to scroll set to something other than the default three. So the if statement calculates the distance. I left it in there though in case other people stumble on this question and it is important to them though.
$('body').bind('mousewheel DOMMouseScroll', function(e) {
var scrollTo = null;
if (e.type == 'mousewheel') {
scrollTo = (e.wheelDelta * -1);
}
else if (e.type == 'DOMMouseScroll') {
scrollTo = 40 * e.detail;
}
//adjust value of scrollTo here if you like.
scrollTo = 16;
if (scrollTo) {
e.preventDefault();
$(this).scrollTop(scrollTo + $(this).scrollTop());
}
});

Coming from another programming language I also found JavaScript difficult when dealing with UI. In your case I would just set a handler to the event onscroll and query the position of the div relative to the scroll position. Return false whenever position of div is not divisible by 16px and create a counter to allow reposition after another 16px is scrolled.