Intoduction to functional programming in JS - Solutions

buildTree

const buildTree = (list, parent) => {
        var node = {}
        list
            .filter(x => x.parent === parent)
            .forEach(x => {
                node[x.id] = buildTree(list, x.id)
            })
        return node
    }
    // { autofold
module.exports = {
    buildTree: buildTree
};
// }

A pure functional version:

const buildTree = (list, parent) => {
	return list
	.filter(p => p.parent === parent)
	.reduce((children, child) => {
		children[child.id] = buildTree(list, child.id);
		return children;
	},{});
}

How about this

const buildTree = (list, parent) => {
  return list.reduce((acc, curr) => {
    if (curr.parent === parent) {
      acc[curr.id] = buildTree(list, curr.id);
    }
    return acc;
  }, {});
}

It also works with map:

const buildTree = (list, parent) => { 
    let familytree = {}
    list.filter(x => x.parent === parent)
        .map(x => {
            familytree[x.id] = buildTree(list, x.id)
         })
    return familytree
}