computer-science-in-javascript/encodings/base64/base64.js

Collection of classic computer science paradigms, algorithms, and approaches written in JavaScript.

/*
 * Base 64 implementation in JavaScript
 * Copyright (c) 2009 Nicholas C. Zakas. All rights reserved.
 * 
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 * 
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 * 
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 * THE SOFTWARE.
 */ 
 
/**
 * Base64-encodes a string of text.
 * @param {String} text The text to encode.
 * @return {String} The base64-encoded string.
 */
function base64Encode(text){
        
    if (/([^\u0000-\u00ff])/.test(text)){
        throw new Error("Can't base64 encode non-ASCII characters.");
    }   
 
    var digits = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/",
        i = 0,
        cur, prev, byteNum,
        result=[];      
    
    while(i < text.length){
        
        cur = text.charCodeAt(i);
        byteNum = i % 3;
        
        switch(byteNum){
            case 0: //first byte
                result.push(digits.charAt(cur >> 2));
                break;
                
            case 1: //second byte
                result.push(digits.charAt((prev & 3) << 4 | (cur >> 4)));
                break;
                
            case 2: //third byte
                result.push(digits.charAt((prev & 0x0f) << 2 | (cur >> 6)));
                result.push(digits.charAt(cur & 0x3f));
                break;
        }
        
        prev = cur;
        i++;
    }
    
    if (byteNum == 0){
        result.push(digits.charAt((prev & 3) << 4));
        result.push("==");
    } else if (byteNum == 1){
        result.push(digits.charAt((prev & 0x0f) << 2));
        result.push("=");
    }
 
    return result.join("");
}

/**
 * Base64-decodes a string of text.
 * @param {String} text The text to decode.
 * @return {String} The base64-decoded string.
 */
function base64Decode(text){
        
    //ignore white space
    text = text.replace(/\s/g,"");
        
    //first check for any unexpected input
    if(!(/^[a-z0-9\+\/\s]+\={0,2}$/i.test(text)) || text.length % 4 > 0){
        throw new Error("Not a base64-encoded string.");
    }    

    //local variables
    var digits = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/",
        cur, prev, digitNum,
        i=0,
        result = [];

    //remove any equals signs
    text = text.replace(/=/g, "");
        
    //loop over each character
    while(i < text.length){
        
        cur = digits.indexOf(text.charAt(i));
        digitNum = i % 4;
        
        switch(digitNum){
                
            //case 0: first digit - do nothing, not enough info to work with
            
            case 1: //second digit
                result.push(String.fromCharCode(prev << 2 | cur >> 4));
                break;
                
            case 2: //third digit
                result.push(String.fromCharCode((prev & 0x0f) << 4 | cur >> 2));
                break;
                
            case 3: //fourth digit
                result.push(String.fromCharCode((prev & 3) << 6 | cur));
                break;
        }
        
        prev = cur;
        i++;
    }
    
    //return a string
    return result.join("");

}