Develop Reference

Make a div bigger and wider while scrolling

How do I enlarge a div while scrolling from a size of 20% width and height in the center to 100% width and height?
I'm currently trying at my first website and I'm almost there. All that is missing is animations and improvements in CSS. One of my ideas is that you have a div with a background inside and while scrolling the picture gets bigger up to the whole viewpoint. I would be very grateful if someone could help me.

You can use transform scale to do it.
CSS part will set the element to take 100% of width and height (i use viewport units), and set it position to fixed (so you will see what happen when you scroll).
Since we gonna change it's scale while scroll, set it initial scale to be 20% of it's original size.
JS part will listen to scroll event and scale the div that it won't be less then 20% but also won't be larger then 100%.
Play with the numbers on the condition to get what you need:
const demoDiv = document.querySelector("#demo");
window.addEventListener('scroll', function() {
if (pageYOffset*0.0001 > 1 || pageYOffset*0.0001 < 0.2) { return; }
else { demo.setAttribute('style', 'transform: scale('+pageYOffset*0.0001+');'); }
});
body {height: 40000px; margin: 0; padding: 0;}
p {position: fixed; top: 0; left: 0; font-size: 40px;}
#demo {
text-align: center;
font-size: 10vw;
position: fixed; top: 0; left: 0;
width: 100vw;
height: 100vh;
background-color: black;
color: white;
transform: scale(0.2); /* since you ask for 20% */
}
<p style="">Scroll to see it grow.</p>
<div id="demo">My minumum width and height are 20% and i will stop grow when i get to 100%</div>

Firstly, Congratulations on your first website. Good luck on your coding journey.
You can do it by using CSS & JavaScript. There is many way, but I'm writing one here. I hope it will be some good.
Let us call the div with an CSS ID animatedDiv.
<div id="animatedDiv"></div>
Now, lets style it with CSS
#animatedDiv
{
margin-top: 200px;
background: #dc143c;
min-height: 350px;
min-width: 20%;
position: absolute;
}
Here, I gave the div a background color, Absolute type of position, and margin-top of 200px. You can change it according to your needs. I used min-height and min-width property because these value will not be any fixed value, they will change on scroll.
Now, lets write some JavaScript
var aDiv = document.getElementById("animatedDiv");
function changeWidth()
{
var scrollVal = window.pageYOffset;
var scrollSlow = (scrollVal / 4);
//Changing CSS Width
aDiv.style.width = Math.min(Math.max(scrollSlow, 20), 100) + "%";
}
window.addEventListener('scroll', function()
{
requestAnimationFrame(changeWidth);
}, false);
Here, on a user define function, I catch the div with it's ID and assign into aDiv variable. Then I catch the page offset on Y axis (How much pixel the page was scrolled) and store it into a variable scrollVal, Next I divide the value by four (you can use 5, 10 20). It will slow the changing effect.
I've use Math methods (min and max) to assign a value between 20 to 100%.
To make the function work on scroll, window.addEventListener is used, and the window.requestAnimationFrame() method will tell the browser that we wish to perform it as an animation.
I hope it will be some help to you. I don't know did I explain well the process to you or not. English is not my mother language, so please don't mind if I made any grammatically mistake.
Wish you all the best.

CSS calc and JS calculate are not equal each other

I calculate item width in css , and do the same in js.
First one for element style, second one for carousel track calculation.
My CSS:
.category-carousel .carousel-item {
width: calc((100vw - 80px) / 7); // result is 262.544px
}
and my JS:
var itemWidth = (window.innerWidth - 80) / 7; // result is 262.857px
Result is 262.544 and 262.857.
(I use more then 200 elements , so 200 * 0.313 give me 62px of issue)
Why its work this way ?
DEMO
https://jsfiddle.net/2nwLq7vd/5/
Width and console result are not equal

You can what I changed in your code it is regarding to border padding when set 0 then it give to me same value You should add border, margin in your js calculation for each element

It is because of the border you have set, please refer the image above. You can also find my fiddle here, https://jsfiddle.net/hamzeen/xour0ndm Here is my css:
div {
width: calc((100vw - 80px) / 7);
height: 50px;
display: inline-block;
border: 0px solid;
background-color: red;
}

Set div width that is equal half of window with minus 25px using Javascript or JQuery

I want to subtract 25px or any number of px from two divs that have width set to half of window width
Here is https://jsfiddle.net/vzwa2fjL/8/
Here is what i got so far with JS
$(window).resize(setHeightAndWidth);
$(document).ready(setHeightAndWidth);
function setHeightAndWidth() {
var halfWidth = $('.left, .right').width($(window).width() / 2);
$('.section').height($(window).height());
halfWidth;
}
I just need to do halfWidth - 25px; but i am not sure how.

Use CSS calc with relative viewport width.
Fiddle Demo
.left, .right {
....
width: calc(50vw - 25px);
}
Browser Compatibility
As calc is not reliable to use across mobile browsers, jQuery can be used.
Updated Fiddle
$('.left, .right').width($(window).width() / 2 - 25);
Also,
$('.section').height($(window).height());
is not necessary when the same can be done in CSS.
.section {
height: 100vh;
}

How to user controlled overlap images in JS

I'm desperately searching for solution for my client. I have graphic - something like that:
And I want to be able to take the line with circle in the center and drag it to right or left. And it will be hiding and unhiding my two full images. It's basically two images on the same place, just with another z-index I think.
I think it's possible to do it with JavaScript, but I don't know of any functions or methods for this option.

Here is my solution:
The HTML is pretty simple, just two divs for the images and one for the drag:
<div class="img" id="img1"></div>
<div class="img" id="img2"></div>
<div id="drag"></div>
For the CSS, the important part is to absolute position all the divs and give a background image.
As for the Javascript, with a little help from jQuery, we listen for the mouse events, make some calculations and adjust the CSS of the second image:
$('#drag').on('mousedown', function(e){
var $self = $(this),
dragPos = $self.position().left + $self.width()/2,
imgWidth = $('#img1').width();
$(document).on('mouseup', function(e){
$(document).off('mouseup').off('mousemove');
});
$(document).on('mousemove', function(me){
var mx = me.pageX - e.pageX + dragPos
$self.css({ left: mx });
$('#img2').css({
width: imgWidth - mx,
left: mx,
backgroundPosition: -mx + 'px 0px',
});
});
});
From there, I believe it's pretty easy to customize it and give it a unique look.
Hope this helps!
JsFiddle Demo

Something like this alphamask plugin may do the trick, though I'm not sure how simple it would be for you to implement in the manner of your slider example.

Actually quite simple. The first step is to make it work manually. I'd set it up as follows:
<div class="wrap" id="wrap1">
<div class="img-wrap img1"></div>
<div class="img-wrap img2"></div>
<div>
With CSS as follows:
.wrap {
position: relative;
width: 300px;
height: 300px;
}
.img-wrap {
width: 100%;
height: 100%;
position: absolute;
top: 0px;
left: 0px;
}
.img1 {
z-index: 1;
background: url(bg1.png) no-repeat 0px 0px;
}
.img2 {
z-index: 2;
background: url(bg1.png) no-repeat 0px 0px;
}
Now some JavaScript (with jQuery) to set a position (you can call this when you move a slider over the top later):
function setPosition(percentage){
// get the width of the container
var w = $('#wrap1').width();
// work out the width of left panel
var w1 = Math.floor(w * percentage);
// and the right panel
var w2 = w - w1;
// set the width of the right panel
// move it right by the width of the left panel
// and move the background back by the width of the left panel
$('#wrap1 .img2').css({
width: w2,
left: w1,
backgroundPosition: -w1 + 'px 0px',
});
}
You now just have to decide how to do the dragging. You could even just do it on mouseOver. Easy!

resize image to browser proportionally checking width and height

I'm building a fluid website in which an image must scale to a maximum size depending on the viewport of the browser (minus some margins). I don't want the image to crop or lose its original proportions, so depending on the width or height it should resize to the maximum size possible without cropping.
I wrote some javascript code, but since I'm not a hardcore coder I was wondering how to fix this in the right way. The script works, but has a bug when resizing. It seems that it only processes one if statement when resizing the browser window.
function setSizes() {
var margin_top = 100;
var margin_right = 85;
var margin_bottom = 10;
var margin_left = 85;
// get image width and height
var img_w = $('.gallery_img').width();
var img_h = $('.gallery_img').height();
// calculate viewport width and height
var vp_w = $(window).width() - margin_right - margin_left;
var vp_h = $(window).height() - margin_top - margin_bottom;
//
if (vp_w <= img_w || vp_w > img_w) {
// new width
var img_w_new=vp_w;
// calculate new height
var img_h_new=Math.round((img_h*img_w_new) / img_w);
}
//
if (vp_h <= img_h || vp_h > img_h) {
// new height
var img_h_new=vp_h;
// calculate new width
var img_w_new=Math.round((img_w*img_h_new) / img_h);
}
// change image width and height to new width and new height
$('.gallery_img').width(img_w_new);
$('.gallery_img').height(img_h_new);
}
// onload
$(window).load(function(){ setSizes(); });
// on resize
$(window).bind("resize", function() { setSizes(); });
I searched for a solution for quite some time, but most scripts I found only check and change the width.
Does somebody know how to fix this?
Thanx!

this might be a lame answer but why don't you just use css width setting?
see http://jsfiddle.net/dXm4r/

I think this is a wrong approach? It would be more natural to define width of enclosing container in percents and than define width 100% on image. Something like this:
div.img-container {
width: 30%;
}
div.img-container img {
display: block;
width: 100%;
}
<div class="img-conatiner">
<img src="...
</div>
Please pay attention to the fact that in img CSS rule there is no height specified, this will allow browsers to properly scale image without loosing quality.

You have a line to change the width; simply add a line to change the height, based on your height variable. You can figure out what the height should be by dividing the new width by the old width. Basically, that is the multiple of widths in the new width, which is equal to the multiple of heights in the new height. Therefore, if you multiply that number to the old height, you would get the new height.
Here is the equation you could use:
img_h_new = (img_w_new / img_w) * img_h;
And this is the function you could use with your width function:
$('.gallery_img').height(img_w_new);

http://blog.francois-becker.net/post/2012/08/16/HTMLCSS-container-of-a-maximized-image

you can done it by css ,just apply this css to your image element
.img { /* image*/
position: absolute;
top: 10px;
right: 85px;
bottom: 10px;
left: 85px;
width: calc( 100% - 170px); /* 170 = marging left + right*/
height: calc(100% - 20px); /* 20px = marging top + bottomt*/
background-size: cover;
box-sizing: border-box;
padding: 0px;
}
body { /* container*/
margin: 0px;
padding: 0px;
height: 100%
width:100%;
overflow:hidden;
}
<html>
<body>
<img class="img" src="http://kingofwallpapers.com/picture/picture-004.jpg" > </img>
</body>
</html>