Simon Willison’s Weblog

// First extract the viewbox to get width/height
const svgElement = new DOMParser().parseFromString(
    svgInput, 'image/svg+xml'
).documentElement;
let viewBox = svgElement.getAttribute('viewBox');
[, , width, height] = viewBox.split(' ').map(Number);

// Figure out the width/height of the output image
const newWidth = parseInt(widthInput.value) || 800;
const aspectRatio = width / height;
const newHeight = Math.round(newWidth / aspectRatio);

// Create off-screen canvas
const canvas = document.createElement('canvas');
canvas.width = newWidth;
canvas.height = newHeight;

// Draw SVG on canvas
const svgBlob = new Blob([svgInput], {type: 'image/svg+xml;charset=utf-8'});
const svgUrl = URL.createObjectURL(svgBlob);
const img = new Image();
const ctx = canvas.getContext('2d');
img.onload = function() {
    ctx.drawImage(img, 0, 0, newWidth, newHeight);
    URL.revokeObjectURL(svgUrl);
    // Convert that to a JPEG
    const imageDataUrl = canvas.toDataURL("image/jpeg");
    const convertedImg = document.createElement('img');
    convertedImg.src = imageDataUrl;
    imageContainer.appendChild(convertedImg);
};
img.src = svgUrl;