Tree types

Learn to express tree structures as types.

What are tree types?

A tree type is defined by each node containing a value and an array of child nodes. The cocuklar: Dugum[] field references the same type again; this allows unlimited branching. File systems, categories, and organization structures are modeled this way.

type Node = {
  name: string;
  children: Node[];
};

Tree depth

In a tree type, since each node carries child nodes within itself, the data can be of unlimited depth. Thanks to cocuklar: Dugum[], each child node conforms to the same structure. At leaf nodes, cocuklar is an empty array and branching ends.

Exercise Create a tree object

Define a recursive type named Dugum: { ad: string; cocuklar: Dugum[] }. The kok variable should be of type Dugum with value { ad: "kok", cocuklar: [{ ad: "cocuk1", cocuklar: [] }] }. Print kok.ad with console.log.

Show example solution

type Dugum = {
  ad: string;
  cocuklar: Dugum[];
};
const kok: Dugum = { ad: "kok", cocuklar: [{ ad: "cocuk1", cocuklar: [] }] };
console.log(kok.ad);

Test yourself

What is the cocuklar field of a leaf node in a tree type?
- null
- Itself again
- Empty array []
- undefined
Show answer

Empty array [] — A leaf node has no children, so its cocuklar field is an empty array []; not null or undefined.

Children field type

type Dugum = {
  ad: string;
  cocuklar: ____[];
};

Show answer

type Dugum = {
  ad: string;
  cocuklar: Dugum[];
};

Tree type concepts

cocuklar: Dugum[]

Child node array
ad: string

Node name
yaprak

Childless node
Dugum

Self-referencing type

Next lesson: Deep partial

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