consys - flexible model-constraint checking
**consys** is a flexible tool to evaluate models using generic and readable constraints.
- **Modern & Lightweight:** consys has full TypeScript support and uses no additional dependencies, so it can easily be integrated.
- **Customizable:** Register custom functions and plugins, tailored to the application.
- **Flexible:** Constraints are designed to be as flexible as possible, while still being readable.
- **User friendly:** consys defines its own domain specific language to manage constraints, making it easy to read and fully generic.
## Installation
**consys** is distributed via [npm](https://www.npmjs.com/package/consys), it can be installed using the following command:
```console
npm install consys
```
## Quick start
After the installation, you can start using it. Here is a small example to get you started:
```typescript
// First import the package
import {ConstraintSystem} from 'consys';
// This is our simple model, with an id and age entry
type TableRow = {
id: number;
entryAge: number;
};
// Now, lets create our constraint system
const rowConstraints = new ConstraintSystem();
// For our constraint, we choose a simple assertion that must always be true:
rowConstraints.addConstraint({
constraint: 'ALWAYS: $entryAge < 21',
message: 'Row (id: $id): Age is $entryAge, but it must be 20 or lower.',
});
// Before we can evaluate something, we need to create some instances of our model
let rows: TableRow[] = [
{id: 0, entryAge: 42},
{id: 1, entryAge: 16},
{id: 2, entryAge: 1337},
];
// Lets evaluate our model instance
let reports = rowConstraints.evaluate(rows, {});
for (let report of reports) {
// Since we have only one constraint, there is only one evaluation
let evaluation = report.evaluation[0];
// Now print all errors
if (!evaluation.consistent) {
console.log(evaluation.message);
}
}
```
Output:
```console
>> Row (id: 0): Age is 42, but it must be 20 or lower.
>> Row (id: 2): Age is 1337, but it must be 20 or lower.
```
## Documentation
For a more detailed look into all of the features, including the constraint syntax, custom functions, plugins and more, please have a look into the [wiki](https://github.com/FireboltCasters/consys/wiki).
## Related packages
You might also want to take a look at [consys-solver](https://github.com/FireboltCasters/consys-solver), which is a tool built upon consys that can find feasible models for constraint systems.
## Contributors
The FireboltCasters
