chasovoy85

function getTree(flatTree) {
	// node["1"] is node.index
	// node["key"] is node.parent.index

	flatTree.forEach(node => {
		const nodeIndex = node["1"];
		const nodeParentIndex = node["key"];
		
		node.parent = flatTree
			.find(someNode => someNode["1"] === nodeParentIndex);

		node.childrens = flatTree
			.filter(someNode => someNode["key"] === nodeIndex);

		node.siblings = flatTree
			.filter(someNode => someNode["key"] === nodeParentIndex && someNode !== node);
	});

	const rootNode = flatTree.find(obj => obj["1"] === 1);
	return rootNode;
}

const flatTree = [
	{"1": 1, "3": 128, "4": 1, "key": 0},
	{"1": 2, "3":   0, "4": 0, "key": 1},
	{"1": 3, "3":   0, "4": 0, "key": 1},
	{"1": 4, "3":   0, "4": 0, "key": 2},
	{"1": 5, "3":   0, "4": 0, "key": 2},
	{"1": 6, "3":   0, "4": 0, "key": 3},
	{"1": 6, "3":   0, "4": 0, "key": 3},
	{"1": 7, "3":   0, "4": 0, "key": 1}
];

console.log(getTree(flatTree));