atob
函数将把一个Base64编码的字符串解码成一个新的字符串,其中每个字符对应二进制数据中的每个字节。
const byteCharacters = atob(b64Data);
每个字符的代码点(charCode)将是该字节的值。我们可以通过对字符串中每个字符应用.charCodeAt
方法来创建一个字节值数组。
const byteNumbers = new Array(byteCharacters.length);
for (let i = 0; i < byteCharacters.length; i++) {
byteNumbers[i] = byteCharacters.charCodeAt(i);
}
将这个字节值数组转换成真正的类型化字节数组可以通过将其传递给Uint8Array
构造函数来实现。
const byteArray = new Uint8Array(byteNumbers);
将其放入数组并传递给Blob
构造函数,可以将此转换为BLOB。
const blob = new Blob([byteArray], {type: contentType});
上面的代码可以工作。但是,通过分批处理 byteCharacters
而不是一次性处理所有内容,可以稍微提高性能。在我的初步测试中,512字节似乎是一个很好的分片大小。这给出了以下函数。
const b64toBlob = (b64Data, contentType='', sliceSize=512) => {
const byteCharacters = atob(b64Data);
const byteArrays = [];
for (let offset = 0; offset < byteCharacters.length; offset += sliceSize) {
const slice = byteCharacters.slice(offset, offset + sliceSize);
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: contentType});
return blob;
}
const blob = b64toBlob(b64Data, contentType);
const blobUrl = URL.createObjectURL(blob);
window.location = blobUrl;
完整示例:
const b64toBlob = (b64Data, contentType='', sliceSize=512) => {
const byteCharacters = atob(b64Data);
const byteArrays = [];
for (let offset = 0; offset < byteCharacters.length; offset += sliceSize) {
const slice = byteCharacters.slice(offset, offset + sliceSize);
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: contentType});
return blob;
}
const contentType = 'image/png';
const b64Data = 'iVBORw0KGgoAAAANSUhEUgAAAAUAAAAFCAYAAACNbyblAAAAHElEQVQI12P4//8/w38GIAXDIBKE0DHxgljNBAAO9TXL0Y4OHwAAAABJRU5ErkJggg==';
const blob = b64toBlob(b64Data, contentType);
const blobUrl = URL.createObjectURL(blob);
const img = document.createElement('img');
img.src = blobUrl;
document.body.appendChild(img);
atop
seems deprecated. Better useBuffer.from(data ,'base64')
- Florian Falk