We then create a data URL with that scaled image.Īnd finally, we assign that data URL to our preview image and change it from hidden to visible. When that image is loaded, we define the scaling parameters and then redraw the image in a canvas element with the new size. The code at the bottom has a resize method that uses the FileReader API to read the image the user selects from disk and assign it as the src of an image we created. The code here is encapsulated in a custom element using an Enhance single file component.įirst, we add a hidden image tag at the end of the form that will eventually be a preview of the scaled image. You can read more about using the canvas element for this purpose here ( ). In this example, we will use the browser itself, specifically the element to do the image scaling. One downside is the extra dependency and having to ship that code for the library to the client in the first place. The pros are the symmetry between the client side result or the server side result. One good solution might be to send the wasm-vips library to the client and use it inside a worker to run the same scaling in the browser. ![]() There are many ways to scale an image in a browser. So with our non-JavaScript solution in place, we will add our first client side JavaScript enhancement. It also adds a significant delay to the response when submitting to wait for the server to process it.Ī better solution is resizing it in the browser before sending it over the network. Large images can easily exceed this, and the request will fail before your server sees it. It would be better to only send what you need.Īnother problem is that the AWS lambda request has a payload limit of 6 MB maximum. The problem with the server side processing for scaling the image is that you have already sent a larger than necessary image to the server to throw away most of those bits. In Part 1 images were reduced on the server so that large images did not waste space, but more importantly so that we did not have to serve those large images back as part of displaying the user profile. Here in Part 2 we will add some improvement using a little JavaScript. We built it with an HTML first approach so that it will work with no client side JavaScript. ![]() If you missed that post you should read it first and then come back here. In Part 1 of this post we built a form and backend code to accept files and images uploaded from a browser. ![]() By Ryan FebruPhoto by Dominik Dancs on Unsplash
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