js base64转换成文件

function base64ToFile(base64String, fileName, mimeType) {
    // 去除Base64字符串中的数据URL前缀
    const base64Content = base64String.split(',')[1];
    
    // 将Base64字符串转换为ArrayBuffer
    const byteCharacters = atob(base64Content);
    const byteArrays = [];
    for (let offset = 0; offset < byteCharacters.length; offset += 512) {
        const slice = byteCharacters.slice(offset, offset + 512);
        const byteNumbers = new Array(slice.length);
        for (let i = 0; i < slice.length; i++) {
            byteNumbers[i] = slice.charCodeAt(i);
        }
        const byteArray = new Uint8Array(byteNumbers);
        byteArrays.push(byteArray);
    }
    const blob = new Blob(byteArrays, { type: mimeType });

    // 创建一个临时的URL指向该Blob对象
    const url = URL.createObjectURL(blob);

    // 创建一个a标签用于下载文件
    const a = document.createElement('a');
    a.href = url;
    a.download = fileName;
    document.body.appendChild(a);
    a.click();
    document.body.removeChild(a);
    URL.revokeObjectURL(url);
}

// 示例用法
const base64String = 'data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAAUA...'; // 替换为你的Base64字符串
const fileName = 'example.png';
const mimeType = 'image/png';
base64ToFile(base64String, fileName, mimeType);