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- function isValidISBN (isbn) {
- isbn = isbn.replace(/[^\dX]/gi, '');
- if(isbn.length == 10) {
- var chars = isbn.split('');
- if(chars[9].toUpperCase() == 'X') {
- chars[9] = 10;
- }
- var sum = 0;
- for(var i = 0; i < chars.length; i++) {
- sum += ((10-i) * parseInt(chars[i]));
- }
- return (sum % 11 == 0);
- } else if(isbn.length == 13) {
- var chars = isbn.split('');
- var sum = 0;
- for (var i = 0; i < chars.length; i++) {
- if(i % 2 == 0) {
- sum += parseInt(chars[i]);
- } else {
- sum += parseInt(chars[i]) * 3;
- }
- }
- return (sum % 10 == 0);
- } else {
- return false;
- }
- }
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