Processing tree structured data

 // Encapsulate tree data processing
// The core idea : The process of finding the parent node adopt pid To match id If it matches, put the current item push To match chilren Properties of the
// Fixed implementation steps :
// 1. Loop through groups In the form of id As key, Each item itself acts as value Form a new object [ It is convenient to find the parent node ]
// 2. Traversal array With each item in the array pid Go to match the object formed in the first step id If it matches It means its child nodes
// push To chilren Properties of the If it doesn't match Represents itself as the outermost parent node direct push To the tree array of the final output

/**
  const map = {
    '1': {
      id:1,
      pid:null
    },
    '2':{
      id:2
      pid:1
    }
  }
  const arr = [
     {
      id:1,
      pid:null
     },
     {
      pid:1,
      id:2
     }
  ]
 */

function transTree(arr) {
  const treeArr = []
  //  Logical processing 
  const map = {}
  arr.forEach((item) => {
    map[item.id] = item
    map[item.id].children = []
  })
  arr.forEach(item => {
    //  Object value taking skills   If pid As key You can get the value   representative   Match up 
    if (map[item.pid]) {
      map[item.pid].children.push(item)
    } else {
      treeArr.push(item)
    }
  })
  return treeArr
}

export default transTree

//  Is there any other way 
//  Time complexity  o(n)
//  Recursive writing   The function itself calls   As long as there are function calls   Stack pressing operation   Once the maximum memory is exceeded, there will be stack overflow