js中图片等比例缩放

function resizeImage(file, maxWidth, maxHeight, callback) {
    const img = new Image();
    img.src = URL.createObjectURL(file);

    img.onload = function() {
        let width = img.width;
        let height = img.height;

        if (width > height) {
            if (width > maxWidth) {
                height *= maxWidth / width;
                width = maxWidth;
            }
        } else {
            if (height > maxHeight) {
                width *= maxHeight / height;
                height = maxHeight;
            }
        }

        const canvas = document.createElement('canvas');
        canvas.width = width;
        canvas.height = height;
        const ctx = canvas.getContext('2d');
        ctx.drawImage(img, 0, 0, width, height);

        canvas.toBlob(function(blob) {
            callback(blob);
        }, file.type);
    };
}

// 使用示例
const input = document.getElementById('fileInput');
input.addEventListener('change', function(event) {
    const file = event.target.files[0];
    resizeImage(file, 800, 600, function(resizedImageBlob) {
        // 处理缩放后的图像
        console.log(resizedImageBlob);
    });
});