# traverse [![Version Badge][npm-version-svg]][package-url]

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[![npm badge][npm-badge-png]][package-url]

Traverse and transform objects by visiting every node on a recursive walk.

# examples

## transform negative numbers in-place

negative.js

````javascript
var traverse = require('traverse');
var obj = [ 5, 6, -3, [ 7, 8, -2, 1 ], { f : 10, g : -13 } ];

traverse(obj).forEach(function (x) {
    if (x < 0) this.update(x + 128);
});

console.dir(obj);
````

Output:

    [ 5, 6, 125, [ 7, 8, 126, 1 ], { f: 10, g: 115 } ]

## collect leaf nodes

leaves.js

````javascript
var traverse = require('traverse');

var obj = {
    a : [1,2,3],
    b : 4,
    c : [5,6],
    d : { e : [7,8], f : 9 },
};

var leaves = traverse(obj).reduce(function (acc, x) {
    if (this.isLeaf) acc.push(x);
    return acc;
}, []);

console.dir(leaves);
````

Output:

    [ 1, 2, 3, 4, 5, 6, 7, 8, 9 ]

## scrub circular references

scrub.js:

````javascript
var traverse = require('traverse');

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

var scrubbed = traverse(obj).map(function (x) {
    if (this.circular) this.remove()
});
console.dir(scrubbed);
````

output:

    { a: 1, b: 2, c: [ 3, 4 ] }

# methods

Each method that takes an `fn` uses the context documented below in the context
section.

## .map(fn)

Execute `fn` for each node in the object and return a new object with the
results of the walk. To update nodes in the result use `this.update(value)`.

## .forEach(fn)

Execute `fn` for each node in the object but unlike `.map()`, when
`this.update()` is called it updates the object in-place.

## .reduce(fn, acc)

For each node in the object, perform a
[left-fold](http://en.wikipedia.org/wiki/Fold_(higher-order_function))
with the return value of `fn(acc, node)`.

If `acc` isn't specified, `acc` is set to the root object for the first step
and the root element is skipped.

## .paths()

Return an `Array` of every possible non-cyclic path in the object.
Paths are `Array`s of string keys.

## .nodes()

Return an `Array` of every node in the object.

## .clone()

Create a deep clone of the object.

## .get(path)

Get the element at the array `path`.

## .set(path, value)

Set the element at the array `path` to `value`.

## .has(path)

Return whether the element at the array `path` exists.

# context

Each method that takes a callback has a context (its `this` object) with these
attributes:

## this.node

The present node on the recursive walk

## this.path

An array of string keys from the root to the present node

## this.parent

The context of the node's parent.
This is `undefined` for the root node.

## this.key

The name of the key of the present node in its parent.
This is `undefined` for the root node.

## this.isRoot, this.notRoot

Whether the present node is the root node

## this.isLeaf, this.notLeaf

Whether or not the present node is a leaf node (has no children)

## this.level

Depth of the node within the traversal

## this.circular

If the node equals one of its parents, the `circular` attribute is set to the
context of that parent and the traversal progresses no deeper.

## this.update(value, stopHere=false)

Set a new value for the present node.

All the elements in `value` will be recursively traversed unless `stopHere` is
true.

## this.remove(stopHere=false)

Remove the current element from the output. If the node is in an Array it will
be spliced off. Otherwise it will be deleted from its parent.

## this.delete(stopHere=false)

Delete the current element from its parent in the output. Calls `delete` even on
Arrays.

## this.before(fn)

Call this function before any of the children are traversed.

You can assign into `this.keys` here to traverse in a custom order.

## this.after(fn)

Call this function after any of the children are traversed.

## this.pre(fn)

Call this function before each of the children are traversed.

## this.post(fn)

Call this function after each of the children are traversed.


# install

Using [npm](http://npmjs.org) do:

    $ npm install traverse

# license

MIT

[package-url]: https://npmjs.org/package/traverse
[npm-version-svg]: https://versionbadg.es/ljharb/traverse.svg
[deps-svg]: https://david-dm.org/ljharb/traverse.svg
[deps-url]: https://david-dm.org/ljharb/traverse
[dev-deps-svg]: https://david-dm.org/ljharb/traverse/dev-status.svg
[dev-deps-url]: https://david-dm.org/ljharb/traverse#info=devDependencies
[npm-badge-png]: https://nodei.co/npm/traverse.png?downloads=true&stars=true
[license-image]: https://img.shields.io/npm/l/traverse.svg
[license-url]: LICENSE
[downloads-image]: https://img.shields.io/npm/dm/traverse.svg
[downloads-url]: https://npm-stat.com/charts.html?package=traverse
[codecov-image]: https://codecov.io/gh/ljharb/traverse/branch/main/graphs/badge.svg
[codecov-url]: https://app.codecov.io/gh/ljharb/traverse/
[actions-image]: https://img.shields.io/endpoint?url=https://github-actions-badge-u3jn4tfpocch.runkit.sh/ljharb/traverse
[actions-url]: https://github.com/ljharb/traverse/actions
