base64.js

var BASE64_ARRAY = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/=".split("").map(c => c.charCodeAt(0))
var BASE64_ENCODE_TABLE = new Map(BASE64_ARRAY.map((ord, i) => [i, ord]))
var BASE64_DECODE_TABLE = new Map(BASE64_ARRAY.map((ord, i) => [ord, i]))

export function encode(buffer){
    buffer = new Uint8Array(buffer).slice()
    var output = new Uint8Array(Math.ceil(Math.ceil(buffer.length * 4 / 3) / 4) * 4)
    let continuous = Math.floor(buffer.length / 3) * 3

    for (let i = 0; i < continuous; i+=3){
        let k = 4 * i / 3
        output[k] = BASE64_ENCODE_TABLE.get(buffer[i] >> 2)
        output[k+1] = BASE64_ENCODE_TABLE.get((buffer[i] & 0x03) << 4 | buffer[i+1] >> 4)
        output[k+2] = BASE64_ENCODE_TABLE.get((buffer[i+1] & 0x0F) << 2 | buffer[i+2] >> 6)
        output[k+3] = BASE64_ENCODE_TABLE.get(buffer[i+2] & 0x3F)
    }

    if (buffer[continuous] != undefined){
        let k = 4 * continuous / 3
        output[k] = BASE64_ENCODE_TABLE.get(buffer[continuous] >> 2)
        if (buffer[continuous+1] == undefined){
            output[k+1] = BASE64_ENCODE_TABLE.get((buffer[continuous] & 0x03) << 4) 
            output[k+2] = BASE64_ENCODE_TABLE.get(64)
        } else {
            output[k+1] = BASE64_ENCODE_TABLE.get((buffer[continuous] & 0x03) << 4 | buffer[continuous+1] >> 4)
            output[k+2] = BASE64_ENCODE_TABLE.get((buffer[continuous+1] & 0x0F) << 2)
        }
        output[k+3] = BASE64_ENCODE_TABLE.get(64)
    }

    return output 
}

export function decode(buffer){
    buffer = new Uint8Array(buffer).slice()
    buffer = buffer.map(v => BASE64_DECODE_TABLE.get(v))
    { let p = buffer.indexOf(64); buffer = buffer.subarray(0, p != -1 ? p : buffer.length)}
    var output = new Uint8Array(3 * buffer.length / 4) 
    let continuous = Math.floor(buffer.length / 4) * 4 
    for (let i = 0; i < continuous; i+=4){
        let k = 3 * i / 4 
        output[k] = buffer[i] << 2 | buffer[i+1] >> 4
        output[k+1] = (buffer[i+1] & 0x0F) << 4 | buffer[i+2] >> 2
        output[k+2] = (buffer[i+2] & 0x03) << 6 | buffer[i+3] 
    }
    if (buffer[continuous] != undefined){
        let k = 3 * continuous / 4 
        output[k] = buffer[continuous] << 2 | buffer[continuous+1] >> 4
        if (buffer[continuous+2] != undefined){
            output[k+1] = (buffer[continuous+1] & 0x0F) << 4 | buffer[continuous+2] >> 2
        }
    }
    return output
}