Object Property Assigner

Companion package to object-property-extractor

A lightweight (no dependencies) tool to assign deeply nested values in JS Objects (or Arrays).

Why?

Consider the object

const data = {
  user: {
    name: { first: 'Jango', last: 'Fett' },
    children: ['Boba', 'Clone 1', 'Clone 2', ...etc],
    weapons: [
      { name: 'Blaster', description: 'For shooting stuff' },
      { name: 'Seismic charge', description: '...BWAAAAAANG' },
    ],
  },
  ...otherProperties,
}

In Javascript, you assign inner object properties via dot notation:

data.user.name.last = "Hutt" 

If you want to assign a property dynamically, you can do this:

const key = "user" 
data[key] = { name: "Boba Fett" } // data.user = { name: "Boba Fett" }

However, you can't do this:

const key = "user.name"
data[key] = "Boba Fett"

This tool allows assignation of deep properties using a single "property path" string.

Installation

yarn add object-property-assigner
// OR
npm install object-property-assigner

Usage

Note: function returns a shallow copy of the input, the original object is unmodified

assign( dataObject, propertyString, newValue, { options } ) (See below for options details)

import assign from "object-property-assigner"

// Using the data object above
data = assign(data, "user.name.first", "Boba") // data.user.name.first = "Boba"

data = assign(data, "user.weapons[1].description", "Pew Pew") // data.user.weapons[1].description = "Pew Pew"

Array handling

In addition to accessing array by index (above), if an array consists of objects, then it's possible to assign a single property for all object in the array.

For example:

data = assign(data, "user.weapons.name", "Laser Gun")
// sets *all* user.weapons.name to "Laser Gun"

Options

The (optional) options object can contain any or all of the following parameters:

• remove -- if true, the property will be deleted rather than assigned (in which case the newValue parameter is ignored)

  assign(data, "user.name.first", null, {remove:true}) // delete user.name.first

• createNew -- (default: true). If a property doesn't exist, it will be created, so set this to false if this behaviour is not desired

  assign(data, "user.kind", "Mandalorian", {createNew: true}) // data.user.kind = "Mandalorian"

  Note: for arrays, if an index is specified higher than the current array length, a new item will be created as the next array item, regardless of how much higher the index is. e.g.

  assign( {myArray: [1, 2, 3]}, "myArray[10]", "New Value")
  // --> {myArray: [1, 2, 3, "New Value"]}

• insert (number) -- (only for arrays). If this property is set, then the new value will be inserted into the array at this position and all other elements shuffled along. e.g.

  assign( {myArray: [1, 2, 3]}, "myArray[1]", "New Value")
  // --> {myArray: [1, "New Value", 2, 3]}

• insertBefore (string) -- (only for objects). If this property is set, then the new value will be inserted before the key specified in insertBefore. e.g.

  assign( {one: 1, two: 2, three: 3}, "myNewValue", 69, {insertBefore: "three"} )
  // --> {one: 1, two: 2, myNewValue: 69, three: 3}

  Please note: Javascript does not guarantee object property order, so this option may yield unpredictable results, especially if using non-standard object keys (e.g. numbers). See here for an explanation of how key ordering is handled.
• insertAfter (string) -- (only for objects). Same as insertBefore, but inserts after a particular object key. Same caveats apply.
• noError -- (default: false). If a property doesn't exist and createNew == false, then an error will be thrown. If you'd rather it just silently ignored the missing property, then set this parameter to true. Note that this is only for errors due to invalid property strings -- other errors might still be thrown.

Testing

A jest test suite is included in the repo. To run: yarn test

See /test/test.ts for the test cases.

Bug report / Feature requests

Please make an issue in the Github repo: https://github.com/CarlosNZ/object-property-assigner