Getting started

Introduction

Take a look at this introduction to have a better idea of what Expry is about.

Overview

In many applications, storing data in databases is essential, whether it comes in the form of relational tables or JSON objects. However, when it comes to storing logic, such as forms and validation rules, the existing databases often fall short.

This is where Expry comes into play. Expry allows you to define logic using a simple JSON syntax and convert it into JavaScript code. You can either define your own mappings from JSON to JavaScript or take advantage of the built-in operators that we provide.

Installation

To install this package you have to run the following command.

npm install @expry/system

Usage

The main function of this package is the createExpry function. It receives an object that defines the operations used to map JSON to JavaScript and returns a function.

import { createExpry, Executions } from "@expry/system";

type Operations = {
  concat: {
    params: unknown[];
    return: string;
  };
  gte: {
    params: [unknown, unknown];
    return: boolean;
  };
};

const operations: Executions<Operations> = {
  concat: (args, vars, expry) => {
    const array = args.map((str) => expry(str, vars)) as string[];
    return array.join("");
  },
  gte: (args, vars, expry) => {
    const a = expry(args[0], vars) as number;
    const b = expry(args[1], vars) as number;
    return a >= b;
  },
};

const expry = createExpry<[Operations]>(operations);

The expry function accepts a JSON expression and variables, executes the code that is defined with JSON, and returns the result.

const expression: unknown = {
  name: { $concat: ["$name", " ", "$surname"] },
  adult: { $gte: ["$age", 18] },
};

const variables: Record<string, unknown> = {
  name: "John",
  surname: "Doe",
  age: 20,
};

const result = expry(expression, variables);

console.log(result); // { name: "John Doe", adult: true }

The objects that have a single key starting with $ are the operators used to map JSON to JavaScript code. The strings that start with $ are variables.

Tutorial