I did not find on the internet a mask in the format BBB-1234 for car signs, the ones I found only validate when the field loses focus and even then only say if it is valid or invalid .
You would need something in the first 3 characters to accept letters, add the dash, and, in the next 4 characters, only accept numbers.
You can use the RobinHerbots inputmask plugin in addition to jquery add the jquery.inputmask.bundle.js file.
The mask code is composed of three letters (% w / o%) one stroke (% w / o%) and four digits (% w / o%)
javascript:
$(document).ready(function(){
$("#placa").inputmask({mask: 'AAA-9999'});
});
html:
<input type="text" id="placa" >
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