json-expression-eval

json-expression-eval

A Node.js module that evaluates a json described boolean expression using dynamic functions

Installation

npm install json-expression-eval --save
yarn add json-expression-eval

Usage

• Please see example dir for extended usage and opinionated usage

API

This module enables you to evaluate boolean expressions which are described using a JSON structure and can utilize user defined 'functions'.
There are 4 types op operators you can use:

• and - accepts a non empty list of operators
• or - accepts a non empty list of operators
• not - accepts another operator
• <user defined funcs> - accepts any type of argument and evaluated by the user defined functions and given context.

Example expressions, assuming we have the user and maxCount user defined functions in place can be:

{  
   "or":[  
      {  
         "not":{  
            "user":"[e-mail]"
         }
      },
      {  
         "maxCount":1
      }
   ]
}

Javascript

const evaluator = require('json-expression-eval');
const functionsTable = {
	user: (user, context) => {
        return context.userId === user;
    },
	maxCount: (maxCount, context) => {
        return context.times < maxCount;
    }
};
const result = evaluator.evaluate({or:[{user: '[e-mail]'},{not: {and: [{maxCount: 1},{user: '[e-mail]'}]}}]},{userId:'[e-mail]', times: 1},functionsTable);

Output should be 'true'

TypeScript

import { evaluate } from 'json-expression-eval';
const functionsTable : FunctionsTable = {
	user: (user :string , context : { userId: string }): boolean => {
        return context.userId === user;
    },
	maxCount: (maxCount: number, context: { times: number }): boolean => {
        return context.times < maxCount;
    }
};
const result = evaluate({or:[{user: '[e-mail]'},{not: {and: [{maxCount: 5},{user: '[e-mail]'}]}}]},{userId:'[e-mail]', times: 1},functionsTable);

Output should be 'false'

Test

npm run test