Transforms nested keys of complex objects
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Deep Map Keys

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Install | Usage | API | TypeScript | License

Deep Map Keys recurses through an object and transforms its keys – and the keys of any nested objects – according to some function. Circular references are supported.

To transform the values of an object rather than its keys, use Deep Map.


Install Deep Map Keys via npm.

npm install --save deep-map-keys


Suppose we want to change the keys of an object from snake case to camel case. We can do something like this:

const deepMapKeys = require('deep-map-keys');

let comment = {
  comment_id: 42,
  user_id: 1024,
  user_name: 'Mufasa',
  content: 'You deliberately disobeyed me.',
  viewed_by: [
    { user_id: 3820, user_name: 'Rafiki' },
    { user_id: 8391, user_name: 'Zazu' }

function snakeToCamel(key) {
  return key.replace(/_(\w)/g, (match, char) => char.toUpperCase());

let result = deepMapKeys(comment, snakeToCamel);

And the result will look like this:

  commentId: 42,
  userId: 1024,
  userName: 'Mufasa',
  content: 'You deliberately disobeyed me.',
  viewedBy: [
    { userId: 3820, userName: 'Rafiki' },
    { userId: 8391, userName: 'Zazu' }


deepMapKeys(object, mapFn, [options])


Param Type Description
object any The object whose keys are to be transformed. Typically, this will be a complex object containing other nested objects. This object may be an Array, in which case the keys of any objects it contains will be transformed. The object may contain circular references.
mapFn function The function used to transform each key. The function is called with two arguments:
  • key <string> The key being transformed
  • value <any> The value of the node whose key is being transformed
The return value determines the new name of the key, and must therefore be a string.
[options] object An optional options object. The following option is accepted:
  • thisArg <any=undefined> Sets the value of this within mapFn()


Returns a new object.


TypeScript declarations are included in the package. Just import the module, and things will just work.

The shape of the returned object cannot be inferred from the inputs; however it can be defined by passing a single type argument.

interface Result {
  userName: string;

let result = deepMapKeys<Result>({user_name: 'Pumbaa'}, snakeToCamel);

let name = result.userName; // Everything is OK :)


Copyright © 2016–2019 Akim McMath. Licensed under the MIT License.