It won't recognize the "intQuantity" value when typing a number , just assumes its ALL true =/

<script ="javscript"/>

function checkQuantity()
{

function noCharge(intQuantity){
  if (intQuantity > 100) {
    return true;
  }

  if (intQuantity < 100) {
    return false;
  }

  return true;
}

checkQuantity=parseInt(prompt("Please enter the quantity of light bulbs",""))
if ((intQuantity)==true)
{
    alert("Your light bulbs will arrive shortly. There is NO delivery cha开发者_运维问答rge")
}
else if ((intQuantity)==false)
{
    alert("Your light bulbs will arrive shortly. There will be a  delivery charge of £5.99")
}
else
{
    alert("Please enter an amount")
}
}
</script>

Your code had some bugs.

Check this live example

function checkQuantity() {

    function noCharge(intQuantity) {
        if (intQuantity > 100) {
            return true;
        }

        if (intQuantity < 100) {
            return false;
        }

        return true;
    }

    var amount = noCharge(parseInt(prompt("Please enter the quantity of light bulbs", "")));
    if (amount == true) {
        alert("Your light bulbs will arrive shortly. There is NO delivery charge")
    }
    else if (amount == false) {
        alert("Your light bulbs will arrive shortly. There will be a  delivery charge of £5.99")
    }
    else {
        alert("Please enter an amount")
    }
}

checkQuantity();

Two obvious problems (well, two things collaborating to cause the same bug):

• You're never calling noCharge. Rather than if ((intQuantity) == true), you should be saying if (noCharge(intQuantity) == true) (or, better, if (noCharge(intQuantity))...see below).
• (intQuantity) will be truthy as long as it's not false, null, undefined, or 0. In your case, that's the vast majority of the time.

And a couple of style notes:

• If you're returning a boolean, you don't really have to compare it to anything. Instead of saying if (noCharge(intQuantity) == true, you could just say if (noCharge(intQuantity)). To see if something's false, use the ! operator, like if (!noCharge(intQuantity)).
• You also don't have to compare twice. A boolean is either true or false. The else if... part could be replaced with an else, and you could be rid of the third section altogether.
• Your rules in noCharge are more complicated than they have to be. The current function returns true if, and only if, the quantity is at least 100. Since >= covers that, you could reduce the code to one line: return (intQuantity >= 100).
• Hungarian notation is dead. Let it rest in peace.

With all that fixed:

 function checkQuantity() {
    function noCharge(quantity) {
        return (quantity >= 100);
    }

    var quantity = parseInt(prompt("Quantity:", ""));
    if (noCharge(quantity)) {
        alert("No delivery charge");
    } else {
        alert("Delivery charge of $5.99");
    }
}

Personally i wouldn't even bother with a function for checking whether something is at least 100...but i can see a use for it if the rules ever get more complicated.