使用它将在swal select box init之后调用的didOpen方法

swal({
      title: 'Select field validation',
      input: 'select',
      inputOptions: {
        apples: 'Apples',
        bananas: 'Bananas',
        grapes: 'Grapes',
        oranges: 'Oranges'
      },
      inputPlaceholder: 'Select a fruit',
      showCancelButton: true,
      didOpen: () => {
        $('.swal2-select option:first').attr('disabled', true);
      }
 });