Basic search in a multi level tree

filterTree.js

export function flat (data) {
  return data.reduce((acc, branch) => (!branch.data || branch.data.length === 0)
      ? acc.concat(branch) // Add the branch to the result if no subNodes
      : acc.concat(...flat(branch.data).map(item => ({ // If subNodes, reflat it
        ...item,
        name: `${branch.name}.${item.name}` // Update the names of subNodes to follow the path
      }))), [])
}

export function flatSimple (keyword, tree) {
  return data.reduce((acc, branch) => (!branch.data || branch.data.length === 0)
      ? acc.concat(branch) // Add the branch to the result if no subNodes
      : acc.concat(...flatSimple(branch.data)), [])
}

export function filterTreeSimple (keyword, tree) {
  return flatSimple(tree) // Flat the data
    .filter(branch => branch.name.toLocaleLowerCase().includes(keyword.toLocaleLowerCase())) // Do the filter
}

export default function filterTree (keyword, tree) {
  return flat(tree) // Flat the data
    .filter(branch => branch.name.toLocaleLowerCase().includes(keyword.toLocaleLowerCase())) // Do the filter
}

console.log(filterTree('ni', [{
  name: 'Annie',
  data: [{
    name: 'Paul'
  }]
}, {
  name: 'Jean',
  data: [{
    name: 'Fani'
  }]
}, {
  name: 'Romain'                          
}, {
  name: 'Mami'
}]))