Simple validasi angka

Assalamu'alaikum wr wb.
Kali ini saya akan share bagaimana caranya validasi angka dengan javascript.
Berikut ini syntaxxnya.
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<label>Enter your age: <input type="text" name="age"></label>
<div id="error"></div>

<script>
var input = document.getElementsByName('age')[0]
var errorHolder = document.getElementById('error')

input.onfocus = function() {
  this.style.backgroundColor = ''
  errorHolder.innerHTML = ''
}

input.onblur = function() {
  var age = +this.value
  if (isNaN(age)) {
    this.style.backgroundColor = 'red'
    errorHolder.innerHTML = 'Enter a number please.'
  }
}
</script>

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Semoga bermanfaat.
http://pangeran-it.blogspot.com/