How to use 'rot13 javascript' in JavaScript

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function rot13(str) {
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    let response = [];
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    let strLength = str.length;
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    for (let i = 0; i < strLength; i++) {
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        const char = str.charCodeAt(i);
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        if (char < 65 || (char > 90 && char < 97) || char > 122) {
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            response.push(str.charAt(i));
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        } else if ((char > 77 && char <= 90) || (char > 109 && char <= 122)) {
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            response.push(String.fromCharCode(str.charCodeAt(i) - 13));
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        } else {
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            response.push(String.fromCharCode(str.charCodeAt(i) + 13));
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        }
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    }
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    return response.join("");
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}

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function rot13(string) {
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    return string.replace(/[a-zA-Z]/g, function (c) {
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        return String.fromCharCode((c<="Z"?90:122)>=(c=c.charCodeAt(0)+13)?c:c-26);
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    })
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}