> For the complete documentation index, see [llms.txt](https://structure.js.org/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://structure.js.org/strict-mode.md).

# Strict mode

To instantiate a structure that automatically throws an error if that is invalid, you can use the buildStrict function.

```javascript
const { attributes } = require('structure');
const User = attributes({
  name: {
    type: String,
    required: true,
  },
  age: Number,
})(class User {});

const user = User.buildStrict({
  age: 'Twenty',
});

// Error: Invalid Attributes
// details: [
//   { message: '"name" is required', path: ['name'] },
//   { message: '"age" must be a number', path: ['age'] }
// ]
```

## Custom error

Normally `buildStrict` will throw a default `Error` when attributes are invalid but you can customize the error class that will be used passing a `strictValidationErrorClass` to the *second* parameter of the `attributes` function.

The value of `strictValidationErrorClass` should be a class that accepts an array of erros in the constructor.

```javascript
const { attributes } = require('structure');

class InvalidBookError extends Error {
  constructor(errors) {
    super('Wait, this book is not right');
    this.code = 'INVALID_BOOK';
    this.errors = errors;
  }
}

const Book = attributes(
  {
    name: {
      type: String,
      required: true,
    },
    year: Number,
  },
  {
    strictValidationErrorClass: InvalidBookError,
  }
)(class Book {});

const book = Book.buildStrict({
  year: 'Twenty',
});

// InvalidBookError: Wait, this book is not right
// code: 'INVALID_BOOK'
// errors: [
//   { message: '"name" is required', path: ['name'] },
//   { message: '"year" must be a number', path: ['year'] }
// ]
```


---

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