Package Exports

json-expression-eval

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Readme

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 tests for more usages and example dir for extended 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 (evaluated in that order of precedence):

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.
<compare funcs> - operates on one of the context properties and compare it to a given value.
- {property: {op: value}}
  - available ops:
    - gt - >
    - gte - >=
    - lt - <
    - lte - <=
    - eq - ===
    - neq - !==
- {property: value}
  - compares the property to that value (shorthand to the eq op)

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

{  
   "or":[  
      {  
         "not":{  
            "user":"a@b.com"
         }
      },
      {  
         "maxCount":1
      },
      {  
         "times": { "eq" : 5}
      },
      {  
         "country": "USA"
      }
   ]
}

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: 'a@b.com'},{not: {and: [{maxCount: 1},{user: 'a2@b.com'}]}}]},{userId:'a@b.com', 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: 'a@b.com'},{not: {and: [{maxCount: 5},{user: 'a2@b.com'}]}}]},{userId:'a2@b.com', times: 1},functionsTable);

Output should be 'false'

Test

npm run test