Validaciones
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<input type="email" id="correo" required pattern="^[a-z0-9._%+-]+@[a-z0-9.-]+\.[a-z]{2,4}$" />
var input = document.getElementById('IdOfField');
var validityState_object = input.validity;
document.querySelector( "input" )
.addEventListener( "invalid",
function( event ) {
event.preventDefault();
});
Previene el comportamiento 'default'
Propiedad 'validity'