readme.md

update-diff

Update object by mapping differences with another object. Comes handy for updating state.

let prop = require('update-diff')

let state = {id: 1, values: [1, 2, 3]}

updateDiff(state, {id: 5, values: ['1', '2']}, {
  values: v => {
    if (!v || v.length) throw 'values should be an array-like'
    return Array.from(v, v => parseFloat(v))
  },
  id: id => id
})

// {id: 5, values: [1, 2]}

If property mapper returns any value other than undefined, it is used for new value. undefined keeps state property unchanged. Only primitives get compared in diffing, to compare arrays you have to do it manually:

update(state, opts, {
	positions: (p, state) => {
		if (p.length === state.positions.length) return
		return p
	}
})

To do multipass update, use array of mappers:

let state = {}
let options = {propA: 0, propB: 1, propC: ['foo'], propD: 'bar'}

updateDiff(state, options, [
//first pass mapping
{
  propA: value => value,
  propB: true,
  propC: Array.isArray,
  propD: function () {}
},
//second pass mapping
{
  propX: (x, state) => state.propB + x
},
//third pass mapping
{
  propA: (value, state, options) => state.propA ? 'a' : 'b'
}
])

// {propA: 0, propB: 1, propC: ['foo']}

Related

• obj-map-prop − map object properties by a dict
• map-obj − map properties by single function
• filter-obj − filter properties by single function

Credits

© 2017 Dima Yv. MIT License