Checking if window size has changes and performance/optimalization - javascript

today I'm implementing slider plugin and I have one question about it:
I want to make it responsive, but to achive that (depending on my current implementation) I should add another function which will detect if browser window size has changed - and here's my question - is it good for overall performance? Or maybe I should re-think about my solution and try to build it with pure css?

The browser resize is only temporary and personally I don't see the big hassle for a slight hiccup in that phase.
Since you refer to jquery, you can just add
$(window).resize(function() { ... });
Add it withing the document ready, and you will do good to call it one on load. Just do
$(window).resize();
As far as performance, you are correct that every little addon will have effect on the performance, but only when it is active. When the window is not resized, teh event does not get fired.

<div id="resized"></div>
function display() {
var p = document.createElement("p");
p.textContent = "resize event";
document.getElementById("resized").appendChild(p);
}
$(window).on("resize", display);
or using javascript
function display() {
var p = document.createElement("p");
p.textContent = "resize event";
document.getElementById("resized").appendChild(p);
}
window.addEventListener("resize", display, false);
on jsfiddle

Related

Different Approach to Hiding image in Javascript

I'm responsible for developing an approach/algorithm to hide image on the trigger. But hiding should be in such a way that it would be hard for developers to do "inspect code" and change certain javascript variables or setting some condition true. So visibility:hidden is a no for sure because it's easy to get rid of it through "inspect code".
Only viable option I can think of is injecting image code () through JQuery which would make it quite work for someone to trigger it manually (I believe). But not sure if it's good enough.
What kind of an approach I can implement? Every opinion counts. Thank you.
To clarify: there are 2 images. each button hover will trigger visibility of one of the images. And the goal is to forbid the user from viewing both of them simultaneously. And they may avoid this by changing script conditions and variables. How to prevent that happening?
You could use something like the below to detect when someone uses inspect element to completely hide the content they're trying to change.
var currentHtmlContent;
var element = new Image();
var elementWithHiddenContent = document.querySelector("#element-to-hide");
var innerHtml = elementWithHiddenContent.innerHTML;
element.__defineGetter__("id", function() {
currentHtmlContent= "";
});
setInterval(function() {
currentHtmlContent= innerHtml;
console.log(element);
console.clear();
elementWithHiddenContent.innerHTML = currentHtmlContent;
}, 1000);
It will then show the content when they stop inspecting.

How to enforce user must scroll pdf within iframe

I have a pdf file within iframe. I want user to scroll must in pdf file before submitting the form. i am trying with this,
var position = $('#myIframe').contents().scrollTop();
But not working. Please help me Thanks in advance.
If you don't mind making a static height for your iframe, I have a solution for you.
HTML and CSS
1. Wrap your iframe in a div container
2. set heights for both your container and iframe (height of container should be the height you want your frame to be seen and the iframe height should be large enough to show entire pdf.)
3. set container div's overflow to scroll
Now you have a scrollable "iframe".
Javscript
Get container element. (var containerEl = $("#container")[0];)
Write a scroll function. Within the scroll function find if the total height of the element (scrollHeight) is less than or equal to how much has been scrolled (scrollTop) plus the inner height (clientHeight) of the
element. If it is, remove disabled property from button
Here's the fiddle. Made some changes to #mJunaidSalaat's jsfiddle.
Well I've tried almost an hour on this, Researched it, finally coming to a conclusion that Unfortunately this is not possible using this method.
The PDF is usually not a DOM element, it's rendered by PDF reader software. Every browser has its own mechanism for rendering PDFs, there is no standard. In some cases, the PDF might be rendered by PDF.js; in those situations you might be able to detect scrolling. But Adobe Reader, Foxit, and some of the native PDF rendering don't provide that option.
I've also created a Github issue for this. But no use.
Sorry. Please update me if you could find any thing or any workaround.
I've made a Fiddle for your solution. You can disable the submit button for user until user scroll on your iframe.
function getFrameTargetElement(objI) {
var objFrame = objI.contentWindow;
if (window.pageYOffset == undefined) {
objFrame = (objFrame.document.documentElement) ? objFrame.document.documentElement : objFrame = document.body;
}
return objFrame;
}
$("#myIframe").ready(function() {
var frame = getFrameTargetElement(document.getElementById("myIframe"));
frame.onscroll = function(e) {
$('.submitBtn').prop('disabled', false);
}
});
Hope it helps.
try this
$("#myIframe").ready(function() {
var frame = getFrameTargetElement(document.getElementById("myIframe"));
frame.onscroll = function(e) {
$('.submitBtn').prop('disabled', false);
}
});

force DOM redraw with javascript on demand

The title of the question expresses what I think is the ultimate question behind my particular case.
My case:
Inside a click handler, I want to make an image visible (a 'loading' animation) right before a busy function starts. Then I want to make it invisible again after the function has completed.
Instead of what I expected I realize that the image never becomes visible. I guess that this is due to the browser waiting for the handler to end, before it can do any redrawing (I am sure there are good performance reasons for that).
The code (also in this fiddle: http://jsfiddle.net/JLmh4/2/)
html:
<img id="kitty" src="http://placekitten.com/50/50" style="display:none">
<div>click to see the cat </div>
js:
$(document).ready(function(){
$('#enlace').click(function(){
var kitty = $('#kitty');
kitty.css('display','block');
// see: http://unixpapa.com/js/sleep.html
function sleepStupidly(usec)
{
var endtime= new Date().getTime() + usec;
while (new Date().getTime() < endtime)
;
}
// simulates bussy proccess, calling some function...
sleepStupidly(4000);
// when this triggers the img style do refresh!
// but not before
alert('now you do see it');
kitty.css('display','none');
});
});
I have added the alert call right after the sleepStupidly function to show that in that moment of rest, the browser does redraw, but not before. I innocently expected it to redraw right after setting the 'display' to 'block';
For the record, I have also tried appending html tags, or swapping css classes, instead of the image showing and hiding in this code. Same result.
After all my research I think that what I would need is the ability to force the browser to redraw and stop every other thing until then.
Is it possible? Is it possible in a crossbrowser way? Some plugin I wasn't able to find maybe...?
I thought that maybe something like 'jquery css callback' (as in this question: In JQuery, Is it possible to get callback function after setting new css rule?) would do the trick ... but that doesn't exist.
I have also tried to separte the showing, function call and hiding in different handlers for the same event ... but nothing. Also adding a setTimeout to delay the execution of the function (as recommended here: Force DOM refresh in JavaScript).
Thanks and I hope it also helps others.
javier
EDIT (after setting my preferred answer):
Just to further explain why I selected the window.setTimeout strategy.
In my real use case I have realized that in order to give the browser time enough to redraw the page, I had to give it about 1000 milliseconds (much more than the 50 for the fiddle example). This I believe is due to a deeper DOM tree (in fact, unnecessarily deep).
The setTimeout let approach lets you do that.
Use JQuery show and hide callbacks (or other way to display something like fadeIn/fadeOut).
http://jsfiddle.net/JLmh4/3/
$(document).ready(function () {
$('#enlace').click(function () {
var kitty = $('#kitty');
// see: http://unixpapa.com/js/sleep.html
function sleepStupidly(usec) {
var endtime = new Date().getTime() + usec;
while (new Date().getTime() < endtime);
}
kitty.show(function () {
// simulates bussy proccess, calling some function...
sleepStupidly(4000);
// when this triggers the img style do refresh!
// but not before
alert('now you do see it');
kitty.hide();
});
});
});
Use window.setTimeout() with some short unnoticeable delay to run slow function:
$(document).ready(function() {
$('#enlace').click(function() {
showImage();
window.setTimeout(function() {
sleepStupidly(4000);
alert('now you do see it');
hideImage();
}, 50);
});
});
Live demo
To force redraw, you can use offsetHeight or getComputedStyle().
var foo = window.getComputedStyle(el, null);
or
var bar = el.offsetHeight;
"el" being a DOM element
I do not know if this works in your case (as I have not tested it), but when manipulating CSS with JavaScript/jQuery it is sometimes necessary to force redrawing of a specific element to make changes take effect.
This is done by simply requesting a CSS property.
In your case, I would try putting a kitty.position().left; before the function call prior to messing with setTimeout.
What worked for me is setting the following:
$(element).css('display','none');
After that you can do whatever you want, and eventually you want to do:
$(element).css('display','block');

Show viewport value in html with live update on-change

I have a <p> element somewhere on my page, and I want it to contain the viewport value, which I can get with:
<p>
<script>
document.write($(this).width());
</script>
</p>
But it shows it "statically". How can I get this value to update dynamically (showing the live actual value) when I resize the browser viewport?
You will have to attach the function to the resize event of the window.
Check this.
Well, maybe it will be usefull, done it with following code, not shure it's the best solution, but it works! Maybe someone can improve it or suggest another, more simple way.
window.onresize = resize;
function resize() {
var viewPort = $(window).width();
$("#window").text(viewPort);
}

Disable Browser Window Resize

For starters... I have no sinister intention of subjecting users to popups or anything like that. I simply want to prevent a user from resizing the browser window of a webpage to which they've already navigated (meaning I don't have access to / don't want to use window.open();). I've been researching this for quite a while and can't seem to find a straightforward answer.
I felt like I was on track with something along the lines of:
$(window).resize(function() {
var wWidth = window.width,
wHeight = window.height;
window.resizeBy(wWidth, wHeight);
});
...to no avail. I have to imagine this is possible. Is it? If so, I would definitely appreciate the help.
Thanks
You can first determine a definite size.
var size = [window.width,window.height]; //public variable
Then do this:
$(window).resize(function(){
window.resizeTo(size[0],size[1]);
});
Demo: http://jsfiddle.net/DerekL/xeway917/
Q: Won't this cause an infinite loop of resizing? - user1147171
Nice question. This will not cause an infinite loop of resizing. The W3C specification states that resize event must be dispatched only when a document view has been resized. When the resizeTo function try to execute the second time, the window will have the exact same dimension as it just set, and thus the browser will not fire the resize event because the dimensions have not been changed.
I needed to do this today (for a panel opened by a chrome extension) but I needed to allow the user to change the window height, but prevent them changing the window width
#Derek's solution got me almost there but I had to tweak it to allow height changes and because of that, an endless resizing loop was possible so I needed to prevent that as well. This is my version of Dereck's answer that is working quite well for me:
var couponWindow = {
width: $(window).width(),
height: $(window).height(),
resizing: false
};
var $w=$(window);
$w.resize(function() {
if ($w.width() != couponWindow.width && !couponWindow.resizing) {
couponWindow.resizing = true;
window.resizeTo(couponWindow.width, $w.height());
}
couponWindow.resizing = false;
});
If need some particular element to handle resize in some particular mode, and prevent whole window from resizing use preventDefault
document.getElementById("my_element").addEventListener("wheel", (event) =>
{
if (event.ctrlKey)
event.preventDefault();
});

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