// About base64: https://en.wikipedia.org/wiki/Base64 /** * Converts an array of bytes to base64 encoding * @param {ArrayBuffer} binaryData An ArrayBuffer which represents an array of bytes * @returns {string} A string containing the base64 encoding of `binaryData` */ function bufferToBase64(binaryData) { // The base64 encoding uses the following set of characters to encode any binary data as text const base64Table = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/' // Every 3 bytes translates to 4 base64 characters, if we have less than 3 bytes we must append '=' chars as padding const padding = 3 - (binaryData.byteLength % 3) // Create an instance of Uint8Array, to read from the binaryData array buffer const byteView = new Uint8Array(binaryData) let result = '' // Loop through all bytes in the buffer, in increments of 3 bytes for (let i = 0; i < byteView.byteLength; i += 3) { // Get the index for the next 4 base64 chars const char1 = (byteView[i] & 252) >> 2 const char2 = ((byteView[i] & 3) << 4) + ((byteView[i + 1] & 240) >> 4) const char3 = ((byteView[i + 1] & 15) << 2) + ((byteView[i + 2] & 192) >> 6) const char4 = byteView[i + 2] & 63 result += base64Table[char1] + base64Table[char2] + base64Table[char3] + base64Table[char4] } // Add padding '=' chars if needed if (padding !== 3) { const paddedResult = result.slice(0, result.length - padding) + '='.repeat(padding) return paddedResult } return result } export { bufferToBase64 }