IF statement with or conditions (HTML and Javascript)

Question

Why does this not function correctly?

No matter what value you enter it ALWAYS returns "Invalid Ticket Type"

function start() {
  var TickType;
  TickType = document.getElementById("TicketType").value;
  TickType = String(TickType);
  var TicketQty = document.getElementById("TicketQty").value;

  if (TickType != "A" || TickType != "B" || TickType != "C") {
    document.getElementById("msg").innerHTML = "Invalid Ticket Type";
  }

  if (isNaN(TicketQty)) {
    document.getElementById("msg").innerHTML = "Non numeric qty has been entered";
  }

  if (TicketQty < 1 || TicketQty > 100) {
    document.getElementById("msg").innerHTML = "Qty is outside valid range";
  }
}

<h1>Ticket Sales</h1>
<p>Enter the ticket type (A, B or C)</p>
<input type="text" id="TicketType">

<p>Enter the quantity required (1-100)</p>
<input type="text" id="TicketQty">

<p>
  </br>
</p>

<button onclick="start()">Click me</button>
<p id="msg"></p>

Answer 1

Use && instead of ||

if (TickType != "A" || TickType != "B" || TickType !=  "C"){
    document.getElementById("msg").innerHTML = "Invalid Ticket Type";
}

Explanation

When TickType = "A", TickType != "B" and TickType != "C" conditions are true.

Here two of the condition is always true, so it goes into the if statement

NOTE: Add a trim and a parseInt to the vars and value="" to the fields and emptied the message before testing

function start() {
  var TickType = document.getElementById("TicketType").value.trim();
  var TicketQty = parseInt(document.getElementById("TicketQty").value, 10);
  document.getElementById("msg").innerHTML = "";

  if (TickType != "A" && TickType != "B" && TickType != "C") {
    document.getElementById("msg").innerHTML = "Invalid Ticket Type";
  }

  if (isNaN(TicketQty)) {
    document.getElementById("msg").innerHTML = "Non numeric qty has been entered";
  }

  if (TicketQty < 1 || TicketQty > 100) {
    document.getElementById("msg").innerHTML = "Qty is outside valid range";
  }
}

<h1>Ticket Sales</h1>
<p>Enter the ticket type (A, B or C)</p>
<input type="text" id="TicketType" value="" />

<p>Enter the quantity required (1-100)</p>
<input type="text" id="TicketQty" value="" />

<p><br/></p>

<button onclick="start()">Click me</button>
<p id="msg"></p>