old_contents: 
  // ----------------------------------------------------------------
  // Content Class
  
  class Content {
    static get TYPE_NAME_KEY() {
      return 0;
    }
    
    static get CONTENT() {
      return 'content';
    }
    
    static get ITEM() {
      return 'content-item';
    }
    
    static get HEADER() {
      return 'content-header';
    }
    
    static get ITEM_NAME() {
      return 'content-item-name';
    }
    
    static get ITEM_KEYS() {
      return 'content-item-keys';
    }
    
    static get ITEM_KEY() {
      return 'content-item-key';
    }
    
    static getHeader(_header = null) {
      if (_header != null) {
        return `<div class="${Content.HEADER}">${_header}</div>`
      }
      return '';
    }
    
    static getItemName(_name = null) {
      if (_name != null) {
        return `<div class="${Content.ITEM_NAME}">${_name}</div>`
      }
      return '';
    }
    
    static getItemKey(..._keys) {
      let result = '';
      if (_keys.length > 0 && (_keys.length == 1 && _keys[0] != null)) {
        result += `<div class="${Content.ITEM_KEYS}">`
        for (let i = 0; i < _keys.length; i++) {
          // content-key の作成
          result += `<div class="${Content.ITEM_KEY}">${_keys[i]}</div>`
        }
        result += `</div>`
      }
      return result;
    }
    
    static getItem({
      type = Content.TYPE_NAME_KEY,
      contentId = null,
      header = null,
      name = null,
      keys = null
    } = {}) {
      let result = '';
      
      if (contentId != null) {
        result += `<div class="${Content.CONTENT}" id="${contentId}">`
      }
      if (type == Content.TYPE_NAME_KEY) {
        // content-header の作成
        result += Content.getHeader(header);
        
        // content-item の作成
        result += `<div class="${Content.ITEM}">`
        
        // content-name の作成
        result += Content.getItemName(name);
        
        // content-keys の作成
        result += Content.getItemKey(keys);
        
        result += `</div>`
      }
      if (contentId != null) {
        result += `</div>`
      }
      return result;
    }
  }
  
new_contents: 
  // ----------------------------------------------------------------
  // Content Class
  
  class Content {
    static get TYPE_NAME_KEY() {
      return 0;
    }
    
    static get CONTENT() {
      return 'content';
    }
    
    static get ITEM() {
      return 'content-item';
    }
    
    static get HEADER() {
      return 'content-header';
    }
    
    static get ITEM_NAME() {
      return 'content-item-name';
    }
    
    static get ITEM_KEYS() {
      return 'content-item-keys';
    }
    
    static get ITEM_KEY() {
      return 'content-item-key';
    }
    
    static getContent(_id = null) {
      if (_id != null) {
        return `<div class="${Content.CONTENT}" id="${_id}"></div>`
      }
      return '';
    }
    
    static getHeader(_header = null) {
      if (_header != null) {
        return `<div class="${Content.HEADER}">${_header}</div>`
      }
      return '';
    }
    
    static getItemName(_name = null) {
      if (_name != null) {
        return `<div class="${Content.ITEM_NAME}">${_name}</div>`
      }
      return '';
    }
    
    static getItemKey(..._keys) {
      let result = '';
      if (_keys.length > 0 && (_keys.length == 1 && _keys[0] != null)) {
        result += `<div class="${Content.ITEM_KEYS}">`
        for (let i = 0; i < _keys.length; i++) {
          // content-key の作成
          result += `<div class="${Content.ITEM_KEY}">${_keys[i]}</div>`
        }
        result += `</div>`
      }
      return result;
    }
    
    static getItem({
      type = Content.TYPE_NAME_KEY,
      contentId = null,
      header = null,
      name = null,
      keys = null
    } = {}) {
      let result = '';
      
      if (contentId != null) {
        result += `<div class="${Content.CONTENT}" id="${contentId}">`
      }
      if (type == Content.TYPE_NAME_KEY) {
        // content-header の作成
        result += Content.getHeader(header);
        
        // content-item の作成
        result += `<div class="${Content.ITEM}">`
        
        // content-name の作成
        result += Content.getItemName(name);
        
        // content-keys の作成
        result += Content.getItemKey(keys);
        
        result += `</div>`
      }
      if (contentId != null) {
        result += `</div>`
      }
      return result;
    }
  }
  
subject: Add function getContent in Content