Core traversal

Import as import * as t from 'neotraverse'. Each callback receives the context.

map

t.map(obj, fn, options?) runs fn for each node and returns a new object. Update nodes in the result with ctx.update(value).

Example

import * as t from 'neotraverse';

const input = { a: 1, nested: { b: 2 } };
const out = t.map(input, (ctx, x) => {
  if (typeof x === 'number') ctx.update(x * 10);
});
// out → { a: 10, nested: { b: 20 } }
// input is unchanged

Example: scrub circular references

import * as t from 'neotraverse';

const obj = { a: 1, b: 2, c: [3, 4] };
obj.c.push(obj);

const scrubbed = t.map(obj, (ctx) => {
  if (ctx.circular) ctx.remove();
});
// → { a: 1, b: 2, c: [ 3, 4 ] }

forEach

t.forEach(obj, fn, options?) is like t.map, but ctx.update() mutates obj in place (returns the same reference).

Example

import * as t from 'neotraverse';

const obj = [5, 6, -3, [7, 8, -2, 1], { f: 10, g: -13 }];

t.forEach(obj, (ctx, x) => {
  if (x < 0) ctx.update(x + 128);
});
// → [ 5, 6, 125, [ 7, 8, 126, 1 ], { f: 10, g: 115 } ]

reduce

t.reduce(obj, fn, init?, options?) is a left-fold over every node. Omit init to start from the root and skip the root node in the fold.

See Query → reduce for a seeded example.

paths · nodes

t.paths(obj, options?) and t.nodes(obj, options?) return every non-cyclic path or every node.

For lazy alternatives, see Iteration.

clone

t.clone(obj, options?) deep-clones. Handles circular references, Date/RegExp/Error/typed arrays, and Map/Set (entries deep-cloned), and is prototype-pollution-safe. See Types & traversal.

Example

import * as t from 'neotraverse';

const live = { count: 0 };
const snapshot = t.clone(live);
snapshot.count = 99;
live.count; // 0, unchanged

get · set · has

t.get(obj, path, options?), t.set(obj, path, value, options?), and t.has(obj, path, options?) read / write / test at an array path. get/has only follow own properties; set refuses prototype-polluting keys.

For string paths, see Paths & metrics → getPath.

Example

import * as t from 'neotraverse';

const obj = { a: { b: 1 } };
t.get(obj, ['a', 'b']); // 1
t.set(obj, ['a', 'b'], 2);
t.has(obj, ['a', 'c']); // false