This JavaScript code snippet helps you to create an image crop functionality on a webpage. It comes with a basic UI where users can input an image file to the crop box and adjust the cropping area with zooming buttons. The crop function draws the image on the HTML canvas element and saves the cropped area.
This image crop plugin is best for cropping profile images before uploading. You can transfer the Blob data of the image to the server for uploading.
How to Create Crop Image Functionality in JavaScript
First of all, create the HTML structure for the image crop as follows:
<div class="container">
<div class="imageBox">
<div class="thumbBox"></div>
<div class="spinner" style="display: none">Loading...</div>
</div>
<div class="action">
<input type="file" id="file" style="float:left; width: 250px">
<input type="button" id="btnCrop" value="Crop" style="float: right">
<input type="button" id="btnZoomIn" value="+" style="float: right">
<input type="button" id="btnZoomOut" value="-" style="float: right">
</div>
<div class="cropped">
</div>
</div>
<script type="text/javascript">
window.onload = function() {
var options =
{
imageBox: '.imageBox',
thumbBox: '.thumbBox',
spinner: '.spinner',
imgSrc: 'avatar.png'
}
var cropper;
document.querySelector('#file').addEventListener('change', function(){
var reader = new FileReader();
reader.onload = function(e) {
options.imgSrc = e.target.result;
cropper = new cropbox(options);
}
reader.readAsDataURL(this.files[0]);
this.files = [];
})
document.querySelector('#btnCrop').addEventListener('click', function(){
var img = cropper.getDataURL()
document.querySelector('.cropped').innerHTML += '<img src="'+img+'">';
})
document.querySelector('#btnZoomIn').addEventListener('click', function(){
cropper.zoomIn();
})
document.querySelector('#btnZoomOut').addEventListener('click', function(){
cropper.zoomOut();
})
};
</script>
</body>
Now, style the image crop UI using the following CSS styles:
.container{
width:400px;
margin:0 auto;
}
.imageBox
{
position: relative;
height: 400px;
width: 400px;
border:1px solid #aaa;
background: #fff;
overflow: hidden;
background-repeat: no-repeat;
cursor:move;
}
.imageBox .thumbBox
{
position: absolute;
top: 50%;
left: 50%;
width: 200px;
height: 200px;
margin-top: -100px;
margin-left: -100px;
box-sizing: border-box;
border: 1px solid rgb(102, 102, 102);
box-shadow: 0 0 0 1000px rgba(0, 0, 0, 0.5);
background: none repeat scroll 0% 0% transparent;
}
.imageBox .spinner
{
position: absolute;
top: 0;
left: 0;
bottom: 0;
right: 0;
text-align: center;
line-height: 400px;
background: rgba(0,0,0,0.7);
}
Finally, add the following JavaScript function for its functionality:
/**
* Created by ezgoing on 14/9/2014.
*/
'use strict';
var cropbox = function(options){
var el = document.querySelector(options.imageBox),
obj =
{
state : {},
ratio : 1,
options : options,
imageBox : el,
thumbBox : el.querySelector(options.thumbBox),
spinner : el.querySelector(options.spinner),
image : new Image(),
getDataURL: function ()
{
var width = this.thumbBox.clientWidth,
height = this.thumbBox.clientHeight,
canvas = document.createElement("canvas"),
dim = el.style.backgroundPosition.split(' '),
size = el.style.backgroundSize.split(' '),
dx = parseInt(dim[0]) - el.clientWidth/2 + width/2,
dy = parseInt(dim[1]) - el.clientHeight/2 + height/2,
dw = parseInt(size[0]),
dh = parseInt(size[1]),
sh = parseInt(this.image.height),
sw = parseInt(this.image.width);
canvas.width = width;
canvas.height = height;
var context = canvas.getContext("2d");
context.drawImage(this.image, 0, 0, sw, sh, dx, dy, dw, dh);
var imageData = canvas.toDataURL('image/png');
return imageData;
},
getBlob: function()
{
var imageData = this.getDataURL();
var b64 = imageData.replace('data:image/png;base64,','');
var binary = atob(b64);
var array = [];
for (var i = 0; i < binary.length; i++) {
array.push(binary.charCodeAt(i));
}
return new Blob([new Uint8Array(array)], {type: 'image/png'});
},
zoomIn: function ()
{
this.ratio*=1.1;
setBackground();
},
zoomOut: function ()
{
this.ratio*=0.9;
setBackground();
}
},
attachEvent = function(node, event, cb)
{
if (node.attachEvent)
node.attachEvent('on'+event, cb);
else if (node.addEventListener)
node.addEventListener(event, cb);
},
detachEvent = function(node, event, cb)
{
if(node.detachEvent) {
node.detachEvent('on'+event, cb);
}
else if(node.removeEventListener) {
node.removeEventListener(event, render);
}
},
stopEvent = function (e) {
if(window.event) e.cancelBubble = true;
else e.stopImmediatePropagation();
},
setBackground = function()
{
var w = parseInt(obj.image.width)*obj.ratio;
var h = parseInt(obj.image.height)*obj.ratio;
var pw = (el.clientWidth - w) / 2;
var ph = (el.clientHeight - h) / 2;
el.setAttribute('style',
'background-image: url(' + obj.image.src + '); ' +
'background-size: ' + w +'px ' + h + 'px; ' +
'background-position: ' + pw + 'px ' + ph + 'px; ' +
'background-repeat: no-repeat');
},
imgMouseDown = function(e)
{
stopEvent(e);
obj.state.dragable = true;
obj.state.mouseX = e.clientX;
obj.state.mouseY = e.clientY;
},
imgMouseMove = function(e)
{
stopEvent(e);
if (obj.state.dragable)
{
var x = e.clientX - obj.state.mouseX;
var y = e.clientY - obj.state.mouseY;
var bg = el.style.backgroundPosition.split(' ');
var bgX = x + parseInt(bg[0]);
var bgY = y + parseInt(bg[1]);
el.style.backgroundPosition = bgX +'px ' + bgY + 'px';
obj.state.mouseX = e.clientX;
obj.state.mouseY = e.clientY;
}
},
imgMouseUp = function(e)
{
stopEvent(e);
obj.state.dragable = false;
},
zoomImage = function(e)
{
var evt=window.event || e;
var delta=evt.detail? evt.detail*(-120) : evt.wheelDelta;
delta > -120 ? obj.ratio*=1.1 : obj.ratio*=0.9;
setBackground();
}
obj.spinner.style.display = 'block';
obj.image.onload = function() {
obj.spinner.style.display = 'none';
setBackground();
attachEvent(el, 'mousedown', imgMouseDown);
attachEvent(el, 'mousemove', imgMouseMove);
attachEvent(document.body, 'mouseup', imgMouseUp);
var mousewheel = (/Firefox/i.test(navigator.userAgent))? 'DOMMouseScroll' : 'mousewheel';
attachEvent(el, mousewheel, zoomImage);
};
obj.image.src = options.imgSrc;
attachEvent(el, 'DOMNodeRemoved', function(){detachEvent(document.body, 'DOMNodeRemoved', imgMouseUp)});
return obj;
};
That’s all! hopefully, you have successfully integrated this image crop functionality into your project. If you have any questions or suggestions, feel free to comment below.
