How I built a fast Device Mockup Generator in Vanilla JS

As frontend developers and designers, presenting our work in beautiful device frames is essential for portfolios and client pitches. I was tired of opening heavy design tools just to wrap a screenshot in a laptop frame, so I built a blazing-fast, client-side Mockup Generator.

The Approach

I built this using 100% Vanilla JS and the HTML5 Canvas API. All image processing happens locally in your browser, ensuring zero server uploads and complete privacy for your unreleased projects.

Here is a quick look at how the core logic draws the user's screenshot onto a device frame canvas:

function generateMockup(screenshotImg, deviceFrameImg, canvas, offsetX, offsetY, width, height) {