js判断是否为图片

function isImageByExtension(filename) {
    const imageExtensions = ['.jpg', '.jpeg', '.png', '.gif', '.bmp', '.webp'];
    const ext = filename.substring(filename.lastIndexOf('.')).toLowerCase();
    return imageExtensions.includes(ext);
}

function isImageByMimeType(file) {
    const imageTypes = ['image/jpeg', 'image/png', 'image/gif', 'image/bmp', 'image/webp'];
    return imageTypes.includes(file.type);
}

function isImageByFileReader(file) {
    return new Promise((resolve, reject) => {
        const reader = new FileReader();
        reader.onloadend = () => {
            const arr = (new Uint8Array(reader.result)).subarray(0, 4);
            let header = '';
            for (let i = 0; i < arr.length; i++) {
                header += arr[i].toString(16);
            }
            const imageHeaders = ['ffd8ffe0', 'ffd8ffe1', 'ffd8ffe2', '89504e47', '47494638', '52494646'];
            resolve(imageHeaders.includes(header));
        };
        reader.onerror = reject;
        reader.readAsArrayBuffer(file.slice(0, 4));
    });
}

function isImageByCanvas(file) {
    return new Promise((resolve, reject) => {
        const img = new Image();
        img.onload = () => resolve(true);
        img.onerror = () => resolve(false);
        img.src = URL.createObjectURL(file);
    });
}