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const addKey = (arr,fn,level=1, parent = null)=>{
  arr.forEach((item,i)=>{
      !item.hasOwnProperty('_level') && (item['_level'] = level);
      !item.hasOwnProperty('_key') && (item['_key'] = `key_${level}_${i}`);
      (!item.children||Array.isArray(item.children)&&!item.children.length) && (item['_isLeaf'] = true);
      item.children && addKey(item.children,fn,level+1,item);
      fn && fn(item,parent)
  })
};