Package Exports

json-expression-eval
json-expression-eval/dist/index.js

This package does not declare an exports field, so the exports above have been automatically detected and optimized by JSPM instead. If any package subpath is missing, it is recommended to post an issue to the original package (json-expression-eval) to support the "exports" field. If that is not possible, create a JSPM override to customize the exports field for this package.

Readme

json-expression-eval

A Fully typed Node.js module that evaluates a json described boolean expressions using dynamic functions and a given context.

The module is strictly typed, ensuring that passed expressions are 100% valid at compile time.

This module is especially useful if you need to serialize complex expressions (to be saved in DB for example)

Installation

npm install json-expression-eval

yarn add json-expression-eval

Usage

Please see tests and examples dir for more usages and examples (under /src)

import {evaluate, Expression, ExpressionHandler, validate, ValidationContext} from 'json-expression-eval';
import {Moment} from 'moment';
import moment = require('moment');

interface IExampleContext {
    userId: string;
    times: number | undefined;
    date: Moment;
    nested: {
        value: number | null;
        nested2: {
            value2?: number;
            value3: boolean;
        };
    };
}

type IExampleContextIgnore = Moment;

type IExampleFunctionTable = {
    countRange: ([min, max]: [min: number, max: number], ctx: { times: number | undefined }) => boolean;
}

type IExampleExpression = Expression<IExampleContext, IExampleFunctionTable, IExampleContextIgnore>; // We pass Moment here to avoid TS exhaustion

const context: IExampleContext = {
    userId: 'a@b.com',
    times: 3,
    date: moment(),
    nested: {
        value: null,
        nested2: {
            value3: true,
        },
    },
};

// For validation we must provide a full example context
const validationContext: ValidationContext<IExampleContext, IExampleContextIgnore> = {
    userId: 'a@b.com',
    times: 3,
    date: moment(),
    nested: {
        value: 5,
        nested2: {
            value2: 6,
            value3: true,
        },
    },
};

const functionsTable: IExampleFunctionTable = {
    countRange: ([min, max]: [min: number, max: number], ctx: { times: number | undefined }): boolean => {
        return ctx.times === undefined ? false : ctx.times >= min && ctx.times < max;
    },
};

const expression: IExampleExpression = {
    or: [
        {
            userId: 'a@b.com',
        },
        {
            and: [
                {
                    countRange: [2, 6],
                },
                {
                    'nested.nested2.value3': true,
                },
            ],
        },
    ],
};

// Example usage 1
const handler =
    new ExpressionHandler<IExampleContext, IExampleFunctionTable, IExampleContextIgnore>(expression, functionsTable);
handler.validate(validationContext); // Should not throw
console.log(handler.evaluate(context)); // true

// Example usage 2
validate<IExampleContext, IExampleFunctionTable, IExampleContextIgnore>(expression, validationContext, functionsTable); // Should not throw
console.log(evaluate<IExampleContext, IExampleFunctionTable, IExampleContextIgnore>(expression, context, functionsTable)); // true

Expression

There are 4 types of operators you can use (evaluated in that order of precedence):

and - accepts a non-empty list of expressions
or - accepts a non-empty list of expressions
not - accepts another expressions
<user defined funcs> - accepts any type of argument and evaluated by the user defined functions and the given context.
<compare funcs> - operates on one of the context properties and compares it to a given value.
- {property: {op: value}}
  - available ops:
    - gt - >
    - gte - >=
    - lt - <
    - lte - <=
    - eq - ===
    - neq - !==
    - regexp: RegExp - True if matches the compiled regular expression.
    - regexpi: RegExp - True if matches the compiled regular expression with the i flag set.
    - nin: any[] - True if not in an array of values. Comparison is done using the === operator
    - inq: any[] - True if in an array of values. Comparison is done using the === operator
    - between: readonly [number, number] (as const) - True if the value is between the two specified values: greater than or equal to first value and less than or equal to second value.
- {property: value}
  - compares the property to that value (shorthand to the eq op)

Nested properties in the context can also be accessed using a dot notation (see example above) In each expression level, you can only define 1 operator, and 1 only

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"
      }
   ]
}