Ampliación de imagen/zoom componente con vainilla JavaScript

<img class="image-zoom-available" src="1.jpg" draggable=false>

El principal JavaScript para lograr este efecto de zoom de imagen.

let settings = {

'magnification':3,

'maskSize': 200
}

// Once our images have loaded let's create the zoom
window.addEventListener("load",()=>{

// find all the images

let images = document.querySelectorAll('.image-zoom-available');

// querySelectorAll produces an array of images that we pull out one by one and create a Zoombini for

Array.prototype.forEach.call(images,(image)=>{


new Zoombini(image);

});
});

// A Zoombini (or whatever you want to call it), is a class that takes an image input and adds the zoomable functionality to it. Let's take a look inside at what it does.
class Zoombini {

// When we create a new Zoombini we run this function; it's called the constructor and you can see it taking our image in from above

constructor(targetImage){


// We don't want the Zoombini to forget about it's image, so let's save that info


this.image = targetImage;


// The Zoombini isActive after it has opened up


 this.isActive = false;


// But as it hasn't been used yet it's maskSize will be 0


this.maskSize = 0;


// And we have to start it's coordinates somewhere, they may as well be (0,0)


this.mousex = this.mousey = 0;





// Now we're set up let's build the necessary compoonents


// First let's clone our original image, I'm going to call it imageZoom and save it our Zoombini


this.imageZoom = this.image.cloneNode();


// And pop it next to the image target


this.image.parentNode.insertBefore(this.imageZoom,this.image);


// Make the zoom image that we'll crop float above it's original sibling


this.imageZoom.style.zIndex = 1;


// We don't want to be able to touch it though, we want to reach whats underneat


this.imageZoom.style.pointerEvents = "none";


// And so we can translate it let's make it absolute


this.imageZoom.style.position = "absolute";





// Now let's scale up our enlarged image and add an event listener so that it resizes whenever the size of the window changes


this.resizeImageZoom();


window.addEventListener("resize", this.resizeImageZoom.bind(this), false);





// Now that we're finishing the constructor we need to addeventlisteners so we can interact with it


// This function is just below, but still exists within our Zoombini


this.UI();


// Finally we'll apply an initial mask at default settings to hide this image


this.drawMask();

}



// resizeImageZoom resizes the enlarged image

resizeImageZoom(){


// So let's scale up this version


this.imageZoom.style.width = this.image.getBoundingClientRect().width*settings.magnification+'px';

}



// This could be inside the constructor but it's nicer on it's own I think

UI(){


this.image.addEventListener('mousemove',(event)=>{



// When we move our mouse the x and y coordinates from the event



// We subtract the left and top coordinates so that we get the (x,y) coordinates of the actualy image, where (0,0) would be the top left



this.mousex = event.clientX - this.image.getBoundingClientRect().left;



this.mousey = event.clientY - this.image.getBoundingClientRect().top;







// if we're not active then don't display anything



if (!this.isActive) return;



// The drawMask() function below displays our the portion of the image that we're interested in



this.drawMask();


});





// When they mousedown we open up our mask


this.image.addEventListener('mousedown',()=>{



// But it can be opening or closing, so let's pass in that information



this.isExpanding = true;



// To do that we start the maskSizer function, which calls itself until it reaches full size



this.maskSizer();



// And hide our cursor (we know where it is)



this.image.classList.add('is-active');


});


// if the mouse is released, close the mask


this.image.addEventListener('mouseup',()=>{



// if it's not expanding, it's closing



this.isExpanding = false;



// if the mask has already expanded we'll need to start another maskSizer to shrink it. We don't run the maskSizer unless the mask is changing



if (this.isActive) this.maskSizer();


});


 // same as above, caused by us moving out of the zoom area


this.image.addEventListener('mouseout',()=>{



this.isExpanding = false;



if (this.isActive) this.maskSizer();


});

 }



// The drawmask function shows us the piece of the image that we are hovering over

drawMask(){


// Let's use getBoundingClientRect to get the location of our images


let image = this.image.getBoundingClientRect();


let imageZoom = this.imageZoom.getBoundingClientRect();


// We'll start by getting the (x,y) of our big image that matches the piece we're mousing over (which we stored from our event listener as this.mousex and this.mousey). This is a clunky bit of code to help the zooms work in a variety of situations.


let prop_x = this.mousex/image.width*imageZoom.width*(1-1/settings.magnification)-image.x-window.scrollX;


let prop_y = this.mousey/image.height*imageZoom.height*(1-1/settings.magnification)-image.y-window.scrollY;


// Shift the large image by that amount


this.imageZoom.style.left = -prop_x+"px";


this.imageZoom.style.top = -prop_y+"px";



// Now we need to create our mask


// First let's get the coordinates of the point we're hovering over


let x=this.mousex*settings.magnification;


let y=this.mousey*settings.magnification;


// And create and apply our clip


let clippy = "circle("+this.maskSize+"px at "+x+"px "+y+"px)";


this.imageZoom.style.clipPath = clippy;


this.imageZoom.style.webkitClipPath = clippy;

}



// We'll use the maskSizer to either expand or shrink the size of our mask

maskSizer(){


// We're in maskSizer so we're changing the size of our mask. Let's make the mask radius larger if the Zoombini is expanding, or shrink it if it's closing. The numbers below might need to be adjusted. It closes faster than it opens


this.maskSize = this.isExpanding ? this.maskSize+35 : this.maskSize-40;


// It has the form of: condition ? value-if-true : value-if-false


// Think of the ? as "then" and : as "else"





// if we've reaached max size, don't make it any larger


if (this.maskSize >= settings.maskSize) {



this.maskSize = settings.maskSize;



// we'll no longer need to change the maskSize so we'll just set this.isActive to true and let our mousemove do the drawing



this.isActive = true;


} else if (this.maskSize<0){



// Our mask is closed



this.maskSize = 0;



this.isActive = false;



this.image.classList.remove('is-active');


} else {



// Or else we haven't reached a size that we want to keep yet. So let's loop it on the next available frame



// We bind(this) here because so that the function remains in context



requestAnimationFrame(this.maskSizer.bind(this));


}


// After we have the appropriate size, draw the mask


this.drawMask();

}
}