source: Dev/trunk/src/client/dojox/validate/isbn.js

define(["dojo/_base/lang", "./_base"], function(lang, validate){

validate.isValidIsbn = function(/* String */value) {
        // summary:
        //              Validate ISBN-10 or ISBN-13 based on the length of value
        // value: String
        //              An ISBN to validate
        // returns: Boolean
        var len, sum = 0, weight;
        if(!lang.isString(value)){
                value = String(value);
        }
        value = value.replace(/[- ]/g,''); //ignore dashes and whitespaces
        len = value.length;

        switch(len){
                case 10:
                        weight = len;
                        // ISBN-10 validation algorithm
                        for(var i = 0; i < 9; i++){
                                sum += parseInt(value.charAt(i)) * weight;
                                weight--;
                        }
                        var t = value.charAt(9).toUpperCase();
                        sum += t == 'X' ? 10 : parseInt(t);
                        return sum % 11 == 0; // Boolean
                        break;
                case 13:
                        weight = -1;
                        for(var i = 0; i< len; i++){
                                sum += parseInt(value.charAt(i)) * (2 + weight);
                                weight *= -1;
                        }
                        return sum % 10 == 0; // Boolean
                        break;
        }
        return false;
};

return validate.isValidIsbn;
});