js网站图片转换

function compressImage(file, maxWidth, maxHeight, quality) {
    return new Promise((resolve, reject) => {
        const img = new Image();
        img.src = URL.createObjectURL(file);
        img.onload = () => {
            const canvas = document.createElement('canvas');
            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;
                }
            }

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

            canvas.toBlob((blob) => {
                if (blob) {
                    resolve(new File([blob], 'compressed.jpg', { type: 'image/jpeg', lastModified: Date.now() }));
                } else {
                    reject(new Error('图片压缩失败'));
                }
            }, 'image/jpeg', quality);
        };
        img.onerror = (error) => reject(error);
    });
}