object-rewrite

object-rewrite

Rewrite Object(s) in place using plugins.

This library is used for doing complex in-memory modifications of data. It allows to define use cases in a dynamic way that allows for powerful abstraction.

Install

npm i --save object-rewrite

Getting Started

const {
  injectPlugin,
  filterPlugin,
  sortPlugin,
  rewriter
} = require('object-rewrite');

const queryDataStore = (fields) => { /* ... */ };

const inject = injectPlugin({
  target: 'idNeg',
  requires: ['id'],
  fn: ({ value }) => -value.id
});
const filter = filterPlugin({
  target: '*',
  requires: ['idNeg'],
  fn: ({ value }) => [-2, -1].includes(value.idNeg)
});
const sort = sortPlugin({
  target: '*',
  requires: ['idNeg'],
  fn: ({ value }) => value.idNeg
});
const rew = rewriter({ '': [inject, filter, sort] }, ['id']);

const desiredFields = ['id'];
const rewInstance = rew.init(desiredFields);

const data = queryDataStore(rewInstance.fieldsToRequest);
// data => [{ id: 0 }, { id: 1 }, { id: 2 }]

rewInstance.rewrite(data);
// data => [{ id: 2 }, { id: 1 }]

Please see the tests for more in-depth examples on how to use this library.

Plugins

There are three types of plugins INJECT, FILTER and SORT.

All plugins require:

• target String: target field relative to the plugin path.
• required Array: required fields relative to the plugin path. Will influence fieldsToRequest.
• fn Function: result of this function is used by the plugin. Signature is fn({ key, value, parents, context }).

Inject Plugin

Used to inject data

• target: field that is created or overwritten
• requires: See above
• fn: return value is used for target

Filter Plugin

Used to filter arrays

• target: array that should be filtered
• required: See above
• fn: target is removed iff function returns false. Similar to Array.filter().

Sort Plugin

Used to sort arrays

• target: array that should be sorted
• required: See above
• fn: called for each object in array. Final array is sorted using the result

Only one sort plugin can be specified per target.

Allows for complex sort comparisons and uses sort-fn.js under the hood (see source code).

rewriter(pluginMap: Object, dataStoreFields: Array)

Used to combine multiple plugins. Plugins can be re-used in different rewriters. Rewriters are then used to modify input data.

Constructor takes in an object that maps absolute paths to plugins and the available dataStoreFields. Could for example re-use a plugin as

const { injectPlugin, rewriter } = require('object-rewrite');

const plugin = injectPlugin(/* ... */);

rewriter({
  '': [plugin],
  nodes: [plugin]
}, [/* data store fields */]);

allowedFields: Array

Fields that are allowed to be requested.

init(fields: Array)

Initialize the rewriter for a specific set of fields.

fieldsToRequest

Exposes fields which should be requested from data store. Dynamically computed fields are excluded since they would not be present in the data store.

rewrite(data: Object/Array, context: Object = {})

Pass in object that should be rewritten. The context allows for additional data to be made available for all plugins.

Notes

Dynamic Keys

Under the hood this library uses object-scan. Please refer to the docs for what key pattern are supported.

Execution Order

Plugins are executed in the order INJECT, FILTER and then SORT.

Plugins within the same type are evaluated bottom-up. While this is less performant, it allows plugins to rely on previous executed plugins of the same type.

Plugins of the same type that operate on the same target are executed in order.