I want to program a JavaScript code which checks the input into an input field if it is a double two-digit HEX value. The input must contain exactly 4 digits and letters between a to f and/or 0 to 9. The following code leads to an error with a four digit input.
function check() {
var input = (document.getElementById("textField").value);
if (input.length == 4 && input.match([A-Fa-f0-9])) { alert("the input matches the requirements");}
else {alert("input is invalid");}
}<input type="text" id="textField">
<button type="button" onclick="check()">check!</button> If you are using regex you can define the length and simplify your test. You need to put your regex string in '/ /'.
if (input.match('/[A-Fa-f0-9]{4}/')) { ... }