javascript 什么是 base64 长度（以字节为单位）？
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What is a base64 length in bytes?
提问by daisy
I have a file encoded in Base64 with a certain file length. How do I get the size in bytes?
我有一个以 Base64 编码的文件，具有一定的文件长度。我如何获得以字节为单位的大小？
Example:
例子：
var size= canvas.toDataURL();
console.log(resizeCanvasURL.length);
// -> 132787 base64 length
回答by mishik
Each symbol in Base64 encoding holds 6 bits of information. Each symbol in normal file hold 8 bits. Since after decoding you have the same amount of information you need:
Base64 编码中的每个符号包含 6 位信息。普通文件中的每个符号占 8 位。由于解码后您拥有所需的相同数量的信息：
normal file size - 1000 bytes
base64 file size - 1333 bytes
回答by Vincent Hoch-Drei
The answer from mishik is wrong.
mishik 的回答是错误的。
Base64 is filled up with =-chars (to have the right amount of bits). So it should be
Base64 用 =-chars 填充（具有正确数量的位）。所以应该是
var byteLength = parseInt((str).replace(/=/g,"").length * 0.75));
