https://github.com/alpacatravel/filter-expressions

Basic array structure that can conditionally evaluate objects
https://github.com/alpacatravel/filter-expressions

Last synced: about 2 months ago
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Basic array structure that can conditionally evaluate objects

• Host: GitHub
• URL: https://github.com/alpacatravel/filter-expressions
• Owner: AlpacaTravel
• License: mit
• Created: 2018-02-04T20:06:59.000Z (almost 7 years ago)
• Default Branch: master
• Last Pushed: 2022-12-03T09:25:22.000Z (about 2 years ago)
• Last Synced: 2024-11-03T22:34:57.212Z (2 months ago)
• Language: JavaScript
• Size: 191 KB
• Stars: 1
• Watchers: 2
• Forks: 0
• Open Issues: 6
• Metadata Files:
  • Readme: README.md
  • License: LICENSE

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README

        
# Overview

Simple util to provide the ability to evaluate targets based on simple evaluation conditions expressed as arrays. Primarily created so that external JSON files can express conditional expressions.

## Example

The below example shows the simple filter expressions on a collection.

```javascript

// Import evaluate from the library

import { evaluate } from 'filter-expressions';

// JSON definition of filter

const json = {

  "filter": [

    "all",

    ["==", "type", "document"],

    ["in", "tags", "example", "other"]

  ]

};

// Example objects

const objects = [

  { type: 'document', tags: ['example'], src: 'https://alpacamaps/document1.json' },

  { type: 'document', tags: ['something'], src: 'https://alpacamaps/document2.json' },

  { type: 'document', tags: ['other'], src: 'https://alpacamaps/document3.json' },

  { type: 'image', tags: ['example'], src: 'https://alpacamaps/image.png' }

];

// Match the objects

const matched = objects.filter(obj => evaluate(json.filter, obj));

// Returns [

//   { type: "document", src: "https://alpacamaps/document1.json", tags: ["example"] },

//   { type: "document", src: "https://alpacamaps/document3.json", tags: ["other"] }

// ]

```

## Installation

You can add this using NPM

```

$ npm install filter-expressions

```

## Supported Comparison Operators

* Existence: exists / exist / !exists / !exist / empty / !empty

* Comparison: == / != / > / >= / < / <=

* Membership: in / !in

* String Comparision: match

* Combining: all / any / none

* Geospatial comparisons: geo-within / geo-contains / geo-disjoint / geo-crosses / geo-overlap

## Extensions

### Custom Comparison Operators

You can provide your own comparison operator implementations.

```javascript

import { evaluate } from 'filter-expressions';

const options = {

  comparisons: {

    custom: (a, b) => a === b,

  },

};

// evaluate(expression, object, [options])

const result = evaluate(['custom', 'foo', 'bar'], { 'foo': 'bar' }, options);

console.log(result); // Prints true

```

### Custom Value Modifiers

You can implement your own value modifiers.

```javascript

import { evaluate } from 'filter-expressions';

const options = {

  modifiers: {

    not: (val) => !val,

  },

};

// evaluate(expression, object, [options])

const result = evaluate(['==', 'not(a)', false], { a: true }, options);

console.log(result); // Prints true

```

### Custom Operators

You can implement custom operators to perform transformations

```javascript

import { evaluate } from 'filter-expressions';

const options = {

  operators: {

    at: (target, index, array) => array && array[index],

    'to-number': (target, val) => Number(val),

  },

};

console.log(evaluate(['at', 1, [2, 4, 6]])); // Prints 4

console.log(evaluate(['to-number', '4'])); // Prints 4

```

## Conversion of query

```javascript

// Import asMongoDbQueryDocument from the library

import { asMongoDbQueryDocument } from 'filter-expressions';

// JSON definition of an expression that can run both on a local collection

const json = [

  "all",

  ["==", "type", "document"],

  ["in", "tags", "example", "other"]

];

// Convert the evaluation into a mongodb query document that can run on

// a mongo db collection

const query = asMongoDbQueryDocument(json);

```

## Notes

* Comparisons are done as using lodash "isEqual".

* Run npm t to run tests

* Inspired based on Mapbox style filters