validate_number.js

let input = $('#txt_number')

function validateNumberKey(e) { //keydown
  let newVal = this.value + e.key
  
  return e.keyCode == 36 || // e.key=Home
    e.keyCode == 8  || // e.key=Backspace
    e.keyCode == 37 || // e.key=ArrowLeft
    e.keyCode == 39 || // e.key=ArrowRight
    $.isNumeric(newVal)
}

input.on('keydown', validateNumberKey)