In order to generate a random string, we must first specify length of string and character set

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function generateRandom(lengthOfString, charset) {
    // The scope of the character
    if(charset == null) charset = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz1234567890';

    var rand = '';

    while(lengthOfString > 0) {
        /*
        since the index of char is start from 0, so no need to +1 on the random number
        we want the range from 0 - lengthOfString
        */
        rand += charset.charAt(Math.floor(Math.random() * charset.length));
        lengthOfString--;
    }
    return rand;
}

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