mapTree

1-map-tree.js

function mapTree(mapper, node) {
	return {
		value: mapper(node.value),
		nodes: node.nodes
			? node.nodes.map( x => mapTree(mapper, x))
			: null
	}
}

2-example-usage.js

let familyTree = {
value: 'mattias',
	nodes: [
		{
			value: 'eva',
			nodes: [
				{ value: 'ove' },
				{ value: 'sonja' }
			]
		},
		{
			value: 'maths',
			nodes: [
				{ value: 'anna' },
				{ value: 'gustav' }
			]
		}
	]
}
mapTree(value => value.toUpperCase(), familyTree)  
/*
OUTPUT:
{
	value: 'MATTIAS',
	nodes: [
		{
			value: 'EVA',
			nodes: [
				{ value: 'OVE' },
				{ value: 'SONJA' }
			]
		},
		{
			value: 'MATHS',
			nodes: [
				{ value: 'ANNA' },
				{ value: 'GUSTAV' }
			]
		}
	]
}
*/