Your JS function should look more like this:
function checkingstring(inputElem) {
var regex = /^[A-Z]{2}[0-9]{4}-[0-9]{5}$/i;
var searchText = inputElem.value;
if (searchText.length && !regex.test(searchText)) {
alert('The syntax is always as follows: AANNNN-NNNNN \n' +
'(A: Alpha/Letter; N: Number), e.g. FL0301-12345');
}
}
You should probably also change the onmousemove
to something more meaningful, like onblur
maybe.
Take a look at this short demo.