js选择本地图片

<input type="file" id="imageInput">
<img id="previewImage" src="" alt="Image Preview">

<script>
document.getElementById('imageInput').addEventListener('change', function(event) {
    const file = event.target.files[0];
    if (file) {
        const reader = new FileReader();
        reader.onload = function(e) {
            document.getElementById('previewImage').src = e.target.result;
        };
        reader.readAsDataURL(file);
    }
});
</script>

<input type="file" accept="image/*">

function compressImage(file, maxWidth, maxHeight) {
    return new Promise((resolve, reject) => {
        const reader = new FileReader();
        reader.onload = function(e) {
            const img = new Image();
            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((blob) => {
                    resolve(new File([blob], file.name, { type: file.type }));
                }, file.type);
            };
            img.src = e.target.result;
        };
        reader.readAsDataURL(file);
    });
}