base_62_converter.js

// JavaScript (ES6) port of the code at https://gist.github.com/bhelx/778542 
// Also handles leading 0's in strings 

const BASE = 62;
const UPPERCASE_OFFSET = 55;
const LOWERCASE_OFFSET = 61;
const DIGIT_OFFSET = 48;

class Base62{
    constructor() {
        
    }

    isDigit(char) {
        return !isNaN(parseInt(char, 10));
    }

    trueOrd(char) {
        if(this.isDigit(char)) {
            return char.charCodeAt(0) - DIGIT_OFFSET;
        } else if(('A' <= char) && (char <= 'Z')) {
            return char.charCodeAt(0) - UPPERCASE_OFFSET;
        } else if(('a' <= char) && (char <= 'z')) {
            return char.charCodeAt(0) - LOWERCASE_OFFSET;
        } else {
            throw new Error(char + " is not a valid character");
        }
    }

    trueChr(int) {
        if(int < 10) {
            return String.fromCharCode(int + DIGIT_OFFSET);
        } else if((10 <= int) && (int <= 35)) {
            return String.fromCharCode(int + UPPERCASE_OFFSET);
        } else if((36 <= int) && (int< 62)) {
            return String.fromCharCode(int + LOWERCASE_OFFSET);
        } else {
            throw new Error(int+" is not a valid integer in the range of base "+ BASE);
        }
    }

    encode(key) {
        const reversed_key = Array.from(key).reverse();
        let int_sum = 0;
        for(const idx of reversed_key.keys()) {
            int_sum += this.trueOrd(reversed_key[idx]) * Number(Math.pow(BASE, idx))
        }
        return int_sum;
    }

    decode(int) {
        if(int == 0) {
            return '0';
        }
        let str = '';
        while(int >= 0) {
            let rem = int % BASE;
            str = this.trueChr(rem) + str;
            if (int === 0)
            {
                break;
            }
            int = Math.floor(int/BASE);
        }
        return str;
    }
}


// let b62 = new Base62();
// console.log(b62.decode(b62.encode('0Zebra'))); // => 0Zebra