Here is the JSfiddle Demo
I changed your HTML and give your input textfield an id of value. I removed the passed param for your verifyorder function, and instead grab the content of your textfield by using document.getElementById(); then i convert the str into value with +order so you can check if it's greater than zero:
<input type="text" maxlength="3" name="value" id='value' />
<input type="button" value="submit" onclick="verifyorder()" />
</p>
<p id="error"></p>
<p id="detspace"></p>
function verifyorder() {
var order = document.getElementById('value').value;
if (+order > 0) {
alert(+order);
return true;
}
else {
alert("Sorry, you need to enter a positive integer value, try again");
document.getElementById('error').innerHTML = "Sorry, you need to enter a positive integer value, try again";
}
}