deep-reduce

Reduce objects deeply, call reducer for every nested node in object tree.

Install

npm i deep-reduce

Usage

const deepReduce = require('deep-reduce')
const deepEqual = require('assert').deepEqual

// let nested leaf values be equal to their path
let deepNestedObject = {
  a: 'a',
  b: { c: 'b.c' },
  c: [
    'c.0',
    {
      d: 'c.1.d',
      e: [
        'c.1.e.0'
      ]
    }
  ]
}

/**
 * Store all values which are strings to reduced[path].
 */
let flattenStrings = (reduced, value, path) => {
  if (typeof value === 'string') {
    reduced[path] = value
  }
  return reduced
}

let reduced = deepReduce(deepNestedObject, flattenStrings)

deepEqual(reduced, {
  'a': 'a',
  'b.c': 'b.c',
  'c.0': 'c.0',
  'c.1.d': 'c.1.d',
  'c.1.e.0': 'c.1.e.0'
})

API

deepReduce takes 5 arguments. 2 mandatory and 3 optional:

deepReduce (obj: object, reducer: ReducerFunction, reduced = {}, path = '', thisArg = {}): any

Arguments:

• obj Object to traverse.

• reducer Function to call with every value in obj-tree. See further below for function signature.

• reduced Initial value of reduced passed to reducer. Default to empty object {}.

• path Path to root, start traversing here. Nice to omit looping through parts of obj.

  Example:

  deepReduce({ a: [1,2,3], b: { c: [3, 3] } }, (reduced, val) => reduced + val, 1, 'b.c')
  // only traverses b.c, returns 1 + 3 + 3 = 7

• thisArg Bound to reducer as this.

Arguments for reducer function: The reducer function are called with these arguments:

interface ReducerFunction {
  (reduced, value, path: string, obj: object): any
}

• reduced Initial or current reduced value.
• value Value of current node.
• path Path to current value.
• obj Root object passed to deepReduce as obj.

The reducer should return the reduced value.

Performance

I have not given performance any thoughs. If you have any ideas, open an issue.

Development

git clone https://github.com/arve0/deep-reduce
cd deep-reduce
npm start  # watches index.ts and builds on any change
npm test  # runs node test.js

License

MIT © 2017 Arve Seljebu