$.fn.extNumber = function(){
  var $this = $(this)
  var $node = $('<a data-ext-number="minus" class="minus">-</a><div class="number"><input data-ext-number="input" /><span>份</span></div><a data-ext-number="plus" class="plus">+</a>')
  $node.appendTo($this)
  
  $this.each(function(){
    var $this = $(this)
    var $extNumberInput = $this.find('[data-ext-number=input]')

    $this.on('click','[data-ext-number=minus]',function(){
      var value = $extNumberInput.val()
      value = !isNaN(+value) ? parseInt(+value) : 0
      $extNumberInput.val(value < 1 ? 0 : value - 1)
    })

    $this.on('click','[data-ext-number=plus]',function(){
      var value = $extNumberInput.val()
      value = !isNaN(+value) ? parseInt(+value) : 0
      $extNumberInput.val(value + 1)
    })
  })
  return this
}

$('#demo1,#demo3').extNumber()