Resize and Rotate Images Using JavaScript

If you are a Web Developer, you may be wondering how you could resize and rotate images. Well, if you are using JavaScript, you are in luck! Resizing and rotating images is entirely possible using JavaScript. Let’s get into it (by the way, this post assumes you have a basic understanding of coding and web development)!

Resizing Images using JavaScript

<img id="container" src="Your image here"/>
#container {
width: 300px;
height: 300px;
border: 1px solid;
document.querySelector('button').onClick = function() {
const image = document.getElementById('container'); = '450px'; = 'auto';

On your page you should see a Resize button which, when clicked, will resize the photo to 450px from 300px. You can easily change the pixel count under to whatever you’d like.

Automated Image Resizing

<input type="file" id="myuploader">
<button onClick='resize()'>Resize</button>
<img id="image">

Next on to the JavaScript:

function resize(){

const resize_width = 600;

const item = document.querySelector('#myuploader').files[0];

const reader = new FileReader();

reader.readAsDataURL(item); =;
reader.size = item.size;
reader.onload = function(event) {
const img = new Image();
img.src =; =;
img.size =;
img.onload = function(el) {
const elem = document.createElement('canvas');

const scaleResize = resize_width /;
elem.width = resize_width;
elem.height = * scaleResize;

const ctx = elem.getContext('2d');
ctx.drawImage(, 0, 0, elem.width, elem.height);

const srcEncoded = ctx.canvas.toDataURL('image/jpeg', 1);

document.querySelector('#image').src = srcEncoded;


If you work through the code, we are setting the image width to 600. We are setting up the File Reader, and getting the data from the image file (the data is being converted into base64 format). We then create a canvas element and scale it with some simple math. Notice the drawImage, which is a specific Canvas method – drawImage “draws” the image thumbnail onto the canvas for us. The data is then encoded. From here one could send off the encoded base64 data to a server, but that is beyond the scope of this post.

Image Resizing with Uploadcare

Let’s take a quick look at how image resize operations would work in Uploadcare. Once you log in to the Dashboard, go to Files; here we can upload an image to Uploadcare.

I’m going to use a cute photo of a puppy that I grabbed for free from Unsplash. Drag an image file to the area indicated on the page. Once the file is uploaded you should see something like this:

Click on the file, and you’ll be taken to the File info screen. As you scroll down you will be able to see some examples of the on the fly image transformations that you can do, on request, with Uploadcare. Since Uploadcare receives requests to transform images via a UUID (an Uploadcare CDN URL), we can take a look at some examples of how one would transform images using Uploadcare via a few UUIDs. It is important to note that when we transform images using Uploadcare, the original image file doesn’t change.

We could rescale an image keeping its original proportions with:


We can resize the photo to 200×200 with:


Lets try Uploadcare’s smart crop function:


Uploadcare also has a smart resize function, an example of this would be:


Zoom In and Out of Images using JavaScript

<div id="wrapper">
<canvas id="myCanvas" width="600" height="600">
<div id="buttonWrapper">
<input type="button" id="plus" value="+"><input type="button" id="minus" value="-">
function myDraw(scale){
const canvas = document.getElementById("myCanvas");
const context = canvas.getContext("2d");
context.clearRect(0, 0, canvas.width, canvas.height);
context.scale(scale, scale);
context.drawImage(image, 0 , 0 , canvas.width, canvas.height);

window.onload = function(){
canvas = document.getElementById("myCanvas");

image = new Image();
image.src = 'Your image here';

document.getElementById("plus").addEventListener("click", function(){
}, false);

document.getElementById("minus").addEventListener("click", function(){
}, false);

image.onload = function () {

You may have noticed, we are essentially scaling an image with Canvas to get the zoom feature. If we just wanted to simply scale an image using Canvas we could do something like this:

<body onload="drawCanvas();">
<canvas id="myCanvas" width="350" height="350"></canvas>
let canvas;
let img;
let x = 50;
let y = 50;

let scale = 0;
let scaleDirection = 0.2;

function drawCanvas() {
canvas = document.getElementById("myCanvas");

if (canvas.getContext) {

img = new Image();
img.onload = loadingComplete;
img.src = "Your Image";

function loadingComplete(e) {
setInterval(loop, 25);

function loop() {
let canvasContext = canvas.getContext('2d');

canvasContext.fillStyle = "rgb(255,255,255)";
canvasContext.fillRect(0, 0, canvas.width, canvas.height);;
canvasContext.translate(x + img.width * 0.5, y + img.height * 0.5);
canvasContext.scale(scale, scale);
canvasContext.translate(-img.width * 0.5, -img.height * 0.5);
canvasContext.drawImage(img, 0, 0);

scale += scaleDirection;
if (scale < 0.2 || scale > 2) {
scaleDirection = -scaleDirection;

The above example uses a loop function and animates our image, scaling it in and out, just to show what you can do with image scaling in a fun way. We could, of course, use buttons to scale instead of an animation. Scaling an image is simply resizing an image. Image software packages use algorithms to assist with scaling images, you can learn more about image scaling here

To zoom an image in Uploadcare you would use crop and then scale the image. An example of how to do this would be the following:

<input type="hidden" role="uploadcare-uploader" name="my_file"
data-crop="400x300 upscale"

Let’s move on to rotating images.

Rotate Images with JavaScript

<img id="turn" onClick="turn(this)" src="Your image here"/>#turn {
transition: all 0.9s ease;
border: 0.0625em solid red;
border-radius: 3.75em;
let turnAngle = 90;function turn(image) {
image.setAttribute("style", "transform: rotate(" + turnAngle + "deg)");
turnAngle = turnAngle + 90;

In addition to the JavaScript logic, the above example relies on the CSS transform property. If you wanted to turn the image upside down, and then rightside up by clicking on it, you can easily modify the code to be 180 degrees instead of 90. You can also customize how fast the image turns by changing the transition property: i.e. if you want it to turn faster you can set it to a lower number for easing.

Rotating Images with Uploadcare


You can also choose autorotation as an option!


Flipping Images

<div id="flip" onmouseover="flip()"><img src="Your Image Here"></div>#flip {
display: block;
width: 50px;
height: 50px;
padding: 25px;
color: white;
font-family: 'Arial', sans-serif;
let k = 0;
function flip() {
let j = document.getElementById("flip");
k += 180; = "rotatey(" + k + "deg)"; = "0.5s"

Flipping images with Uploadcare is as simple as using this command.



And that’s it — congratulations! You’ve learned the basics of image manipulation and transformations with JavaScript and Uploadcare. Give yourself a pat on the back, you’ve earned it!

Written by Maurice Fawcett

File system as a service for web and mobile apps