如何使我的标签字段根据块的下拉选择在Blockly中动态更改

Blockly.Blocks['dynamic_label_block'] = {
  init: function() {
    this.appendDummyInput()
        .appendField("选择选项:")
        .appendField(new Blockly.FieldDropdown([["选项1", "option1"], ["选项2", "option2"], ["选项3", "option3"]]), "dropdown");
    this.appendDummyInput()
        .appendField("标签字段:")
        .appendField(new Blockly.FieldLabel("默认内容"), "label");
    this.setInputsInline(true);
    this.setOutput(true, null);
    this.setColour(230);
    this.setTooltip("");
    this.setHelpUrl("");
  },
  onchange: function(event) {
    if (event.type == Blockly.Events.CHANGE && event.element == 'field' && event.name == 'dropdown') {
      var dropdownValue = this.getFieldValue('dropdown');
      var labelField = this.getField('label');
      switch (dropdownValue) {
        case 'option1':
          labelField.setText("选项1的内容");
          break;
        case 'option2':
          labelField.setText("选项2的内容");
          break;
        case 'option3':
          labelField.setText("选项3的内容");
          break;
        default:
          labelField.setText("默认内容");
          break;
      }
    }
  }
};

Blockly.JavaScript['dynamic_label_block'] = function(block) {
  var dropdown_value = block.getFieldValue('dropdown');
  var code = "'" + dropdown_value + "'";
  return [code, Blockly.JavaScript.ORDER_ATOMIC];
};