Usage no npm install needed!

<script type="module">
  import ucastMongo2js from 'https://cdn.skypack.dev/@ucast/mongo2js';


UCAST Mongo Query to JavaScript Translator

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This package is a part of ucast ecosystem. It combines @ucast/mongo and @ucast/js into a package that allows to evaluate MongoDB query conditions in JavaScript runtime.


npm i @ucast/mongo2js
# or
yarn add @ucast/mongo2js
# or
pnpm add @ucast/mongo2js

Getting Started

To check that POJO can be matched by Mongo Query:

import { guard } from '@ucast/mongo2js';

const test = guard({
  lastName: 'Doe',
  age: { $gt: 18 }

  firstName: 'John',
  lastName: 'Doe',
  age: 19
})); // true

You can also get access to parsed Mongo Query AST:

console.log(test.ast); /*
  operator: 'and',
  value: [
    { operator: 'eq', field: 'lastName', value: 'Doe' },
    { operator: 'gt', field: 'age', value: 18 }

Testing primitives

For cases, when you need to test primitive elements, you can use squire function:

import { squire } from '@ucast/mongo2js';

const test = squire({
  $lt: 10,
  $gt: 18

test(11) // true
test(9) // false

Custom Operator

In order to implement a custom operator, you need to create a custom parsing instruction for MongoQueryParser and custom JsInterpreter to interpret this operator in JavaScript runtime.

This package re-exports all symbols from @ucast/mongo and @ucast/js, so you don't need to install them separately. For example, to add support for json-schema operator:

import { createFilter } from '@ucast/mongo2js';
import Ajv from 'ajv';

const $jsonSchema = {
  type: 'document',
  validate(instruction, value) {
    if (!value || typeof value !== 'object') {
      throw new Error(`"${instruction.name}" expects to receive an object`)
  parse(instruction, schema) {
    const ajv = new Ajv();
    return new DocumentCondition(instruction.name, ajv.compile(schema));
const jsonSchema = (condition, object) => condition.value(object);

const customGuard = createFilter({
}, {
const test = customGuard({
  $jsonSchema: {
    type: 'object',
    properties: {
      firstName: { type: 'string' },
      lastName: { type: 'string' },

console.log(test({ firstName: 'John' })); // false, `lastName` is not defined

TypeScript support

This package is written in TypeScript and supports type inference for MongoQuery:

import { guard } from '@ucast/mongo2js';

interface Person {
  firstName: string
  lastName: string
  age: number

const test = guard<Person>({ lastName: 'Doe' });

You can also use dot notation to set conditions on deeply nested fields:

import { guard } from '@ucast/mongo2js';

interface Person {
  firstName: string
  lastName: string
  age: number
  address: {
    city: string
    country: string

type ExtendedPerson = Person & {
  'address.city': Person['address']['city']

const test = guard<ExtendedPerson>({ lastName: 'Doe' });

Want to help?

Want to file a bug, contribute some code, or improve documentation? Excellent! Read up on guidelines for contributing


Apache License, Version 2.0