isOnlyLettersAndDigits

const isOnlyLettersAndDigits = str => {

    for (let i = 0; i < str.length; i++) {

      let n = str.charCodeAt(i)
      if (!(n >= 97 && n <= 122) && !(n >= 65 && n <= 90) && !(n >= 48 && n <= 57))
        return false
    }

    return true
  }