limiting the value that can be entered in the input

Question

I have a php variable that has a value that varies depending on the moment!! Example

1st moment $valor = 300

second moment $valor = 20

3rd moment $valor = 5300

fourth moment $valor = 1300

I also have an input, in this input can add any value, as long as it is below the value at the time you type. Here’s what I want to do!! If someone comes to enter a higher value in the input the value automatically changes pro maximo and not to what was typed!!

Example:

1st moment $valor = 300 || In this first moment the maximum value of the input may be only 300!! Only instead of 300 the user typed 301, at the same time I want these 301 turn 300, because it is the limit value that the user has!

Answer 1

Using jQuery I created this function that keeps listening to the event keyup (when the user releases a key). Inside the function I check the value.

$('#txtValor').on('keyup', function(event) {
  var valorMaximo = 300;

  if (event.target.value > valorMaximo)
    return event.target.value = valorMaximo;
});

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
Digite o valor: R$ <input type="text" id="txtValor">