Install

This package is pure ESM. If you're not ready yet, install an older version of this program, 2.1.0 (npm i [email protected]).

npm i ast-monkey-traverse-with-lookahead

Quick Take

import { strict as assert } from "assert";

import { traverse } from "ast-monkey-traverse-with-lookahead";

const input = [
  {
    a: "b",
  },
  {
    c: "d",
  },
  {
    e: "f",
  },
];
const gathered = [];

// callback interface:
traverse(
  input,
  (key1, val1, innerObj) => {
    gathered.push([key1, val1, innerObj]);
  },
  1, // <---------------- report one upcoming value
);

assert.deepEqual(gathered, [
  // ===================
  [
    {
      a: "b",
    },
    undefined,
    {
      depth: 0,
      path: "0",
      parent: [
        {
          a: "b",
        },
        {
          c: "d",
        },
        {
          e: "f",
        },
      ],
      parentType: "array",
      next: [
        [
          "a",
          "b",
          {
            depth: 1,
            path: "0.a",
            parent: {
              a: "b",
            },
            parentType: "object",
          },
        ],
      ],
    },
  ],
  // ===================
  [
    "a",
    "b",
    {
      depth: 1,
      path: "0.a",
      parent: {
        a: "b",
      },
      parentType: "object",
      next: [
        [
          {
            c: "d",
          },
          undefined,
          {
            depth: 0,
            path: "1",
            parent: [
              {
                a: "b",
              },
              {
                c: "d",
              },
              {
                e: "f",
              },
            ],
            parentType: "array",
          },
        ],
      ],
    },
  ],
  // ===================
  [
    {
      c: "d",
    },
    undefined,
    {
      depth: 0,
      path: "1",
      parent: [
        {
          a: "b",
        },
        {
          c: "d",
        },
        {
          e: "f",
        },
      ],
      parentType: "array",
      next: [
        [
          "c",
          "d",
          {
            depth: 1,
            path: "1.c",
            parent: {
              c: "d",
            },
            parentType: "object",
          },
        ],
      ],
    },
  ],
  // ===================
  [
    "c",
    "d",
    {
      depth: 1,
      path: "1.c",
      parent: {
        c: "d",
      },
      parentType: "object",
      next: [
        [
          {
            e: "f",
          },
          undefined,
          {
            depth: 0,
            path: "2",
            parent: [
              {
                a: "b",
              },
              {
                c: "d",
              },
              {
                e: "f",
              },
            ],
            parentType: "array",
          },
        ],
      ],
    },
  ],
  // ===================
  [
    {
      e: "f",
    },
    undefined,
    {
      depth: 0,
      path: "2",
      parent: [
        {
          a: "b",
        },
        {
          c: "d",
        },
        {
          e: "f",
        },
      ],
      parentType: "array",
      next: [
        [
          "e",
          "f",
          {
            depth: 1,
            path: "2.e",
            parent: {
              e: "f",
            },
            parentType: "object",
          },
        ],
      ],
    },
  ],
  // ===================
  [
    "e",
    "f",
    {
      depth: 1,
      path: "2.e",
      parent: {
        e: "f",
      },
      parentType: "object",
      next: [],
    },
  ],
  // ===================
]);

Documentation

Please visit codsen.com for a full description of the API. If you’re looking for the Changelog, it’s here.

Contributing

To report bugs or request features or assistance, raise an issue on GitHub.

Licence

MIT License

Copyright © 2010-2025 Roy Revelt and other contributors