condition-flags-parser

JS Condition Parser

Parse/Apply JS-like condition expressions on an object of flags.

Purpose

Easily apply a JS logic condition string based on an array of flags. E.g.: bunch of flags (traits) of a user fetched from a fast backend (e.g. redis). Requested entity requires a bunch of flags with some logic (and, or, threshold) to apply.

Sample flags:

[
    'countryFlag:NL',
    'languageFlag:EN',
    'proUser'
]

Sample condition (logic):

proUser && (countryFlag:NL || languageFlag:NL)

Threshold example (two out of three):

proUser + countryFlag:NL + languageFlag:NL + !optedOut > 2

Support/requirements

Syntax

• Parenthesis is supported
• Valid operators (logic):
  • && (and)
  • || (or)
• Valid threshold operators:
  • + (add)
  • - (subtract)
• Valid comparison operators (for thresholds):
  • > (gt)
  • < (lt)
• Invert
  • ! (not, e.g. flag does not apply, !someFlag)

Flags

• Flags can contain these characters:
  • a-z
  • A-Z
  • 0-9
  • _ (underscore)
  • : (colon)
  • . (dot)
• Flags must start with a-z or A-Z.
• Flags should be present in the condition in plain texts (so no quotes surrounding them)
• Flags are case sensitive

Use

import { validate, flags, apply } from 'condition-flags-parser'

const condition = '(someFlag:123 + anotherFlag) + (countryFlag:NL + !countryFlag:GB) > 3'

// 2nd argument = throw Error in case of validation Error
// Boolean, true if valid, or Throws
console.log(validate(condition, true))

// List flags the condition is working with (for e.g. redis `smismember`)
console.log(flags(condition))

// Returns boolean (condition applies?)
console.log(apply(condition, [
  'someFlag:123',
  'countryFlag:NL',
  'countryFlag:GB',
  'anotherFlag',
]))

Development

Tests: npm run test