Image Aspect Ratio Resizer To 9:16

function processImage(originalImg, fitMode = "cover", backgroundColor = "#000000") {
    const canvas = document.createElement('canvas');
    const ctx = canvas.getContext('2d');

    const w = originalImg.width;
    const h = originalImg.height;
    const orgRatio = w / h;
    
    // 9:16 aspect ratio
    const targetRatio = 9 / 16;

    let cWidth, cHeight;
    let dx = 0, dy = 0;

    // Determine canvas dimensions and image drawing offsets based on fit mode
    if (fitMode.toLowerCase() === "contain") {
        // Pad the image to fit 9:16 without losing any parts of the original image
        if (orgRatio > targetRatio) {
            // Image is proportionally wider than 9:16; we must pad top and bottom
            cWidth = w;
            cHeight = Math.round(w / targetRatio);
            dy = Math.round((cHeight - h) / 2);
        } else {
            // Image is proportionally taller than 9:16; we must pad left and right
            cHeight = h;
            cWidth = Math.round(h * targetRatio);
            dx = Math.round((cWidth - w) / 2);
        }
    } else {
        // Default mode is "cover" - crop the image to fill 9:16 completely
        if (orgRatio > targetRatio) {
            // Image is proportionally wider than 9:16; crop the left and right sides
            cHeight = h;
            cWidth = Math.round(h * targetRatio);
            dx = Math.round(-(w - cWidth) / 2);
        } else {
            // Image is proportionally taller than 9:16; crop the top and bottom sides
            cWidth = w;
            cHeight = Math.round(w / targetRatio);
            dy = Math.round(-(h - cHeight) / 2);
        }
    }

    // Prepare canvas sizes
    canvas.width = cWidth;
    canvas.height = cHeight;

    // Draw background color (visible mostly in 'contain' mode)
    ctx.fillStyle = backgroundColor;
    ctx.fillRect(0, 0, cWidth, cHeight);

    // Draw the image onto the canvas with calculated offsets
    ctx.drawImage(originalImg, dx, dy, w, h);

    return canvas;
}