Structural helpers

Import as import * as t from 'neotraverse'.

deleteWhere · prune

t.deleteWhere returns a new tree with matching nodes removed (map + ctx.remove()). t.prune keeps nodes where the predicate is true (inverse). Map/Set stay whole leaves unless descendIntoMapSet is set.

Example: redact secrets

import * as t from 'neotraverse';

const apiPayload = {
  user: 'alice',
  token: 'secret',
  profile: { email: 'a@example.com', password: 'hunter2' }
};

const safe = t.deleteWhere(
  structuredClone(apiPayload),
  (_, x) => x === 'secret' || x === 'hunter2'
);
// drops matching nodes; original apiPayload unchanged if you cloned first

pruneDeep

Replace nodes deeper than maxDepth with a sentinel (default null). Unlike the maxDepth option, this does not throw.

Example

import * as t from 'neotraverse';

const deep = { a: { b: { c: { d: 1 } } } };
t.pruneDeep(deep, 2);
// → { a: { b: null } } (depth counted from root)

deepEqual

Structural compare with an explicit per-type contract (Dates by time, RegExp by source+flags, etc.). Optional compareFn can override pairs. Not guaranteed to match t.clone() byte-for-byte (e.g. Error fields).

toJSON

JSON.stringify after a walk; circular references become null (configurable via cycle).

Example

import * as t from 'neotraverse';

const graph: any = { name: 'root' };
graph.self = graph;

console.log(t.toJSON(graph)); // {"name":"root","self":null}

freeze

Deep-freeze in place (children before parents). Pair with t.clone when you need an immutable snapshot.

Example

import * as t from 'neotraverse';

const snapshot = t.freeze(t.clone(liveConfig));
// snapshot is deeply frozen; liveConfig can still change

diff · patch

RFC 6902 subset (add / remove / replace). t.diff(a, b) returns ops; t.patch(clone(a), ops) applies them. Acyclic trees only.

Example

import * as t from 'neotraverse';

const v1 = { title: 'Hi', items: [1, 2] };
const v2 = { title: 'Hello', items: [1, 3], extra: true };

const ops = t.diff(v1, v2);
const v2FromV1 = t.patch(structuredClone(v1), ops);
// v2FromV1 deep-equals v2 (acyclic trees)