@ikaru5/heimdall-contract/doc/localization.md

Validation and Representer Objects in your Frontend

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# Localization

There are build-in english simple error messages. You can localize this error messages to your needs.

## i18next

The most of the time you want to use i18next for this. You can find more information about i18next [here](https://www.i18next.com/).
Just tell your base class to use it:

```Javascript
export default class Contract extends ContractBase {
  setConfig() {
    this.contractConfig.localizationMethod = "i18next" // default is "Internal"
    this.contractConfig.i18next = i18n
  }
}
```

## Custom localization method

You can also use your own localization method.

**Warning**: This feature is not final yet. It is ugly to override a private method. So a more elegant solution will be implemented in the future.

Just override the `_getErrorMessageFor` and `_getGenericErrorMessage` method in your base class:

```Javascript
export default class Contract extends ContractBase {
  setConfig() {
    // do not change localizationMethod or i18next config for custom localization method, its simply not needed
    // this.contractConfig.localizationMethod
    // this.contractConfig.i18next
  }
  
  _getErrorMessageFor(propertyValue, propertyConfiguration, dType, depth, validationScope, validationName) {
    return "Some cool error message"
  }

  _getGenericErrorMessage() {
      return "Field invalid!"
  }
}
```

## Custom error messages

You can also set custom error messages for each field. Just use the `errorMessage` property in your field configuration:

```javascript
{
  // one error message for all validations defined for this field
  fieldNameA: {dType: "String", max: 5, min: 3, errorMessage: "Custom error message"},
  // write your own smart error message
  fieldNameB: {dType: "String", max: 5, min: 3, errorMessage: (value, contract, validationName, dType, depth) => "Custom error message"},
  
  // define error messages for each validation rule
  fieldNameB: {dType: "String", max: 5, min: 3, errorMessage:
    {
      min: "Custom min error message",
      max: (value, contract, validationName, dType, depth) => "Custom max error message"
    }
  },

  // you can also define a default error message 
  fieldNameB: {dType: "String", max: 5, min: 3, errorMessage:
    {
      default: "Custom error message, which will be used only for max in this example", // can also be a function
      min: (value, contract, validationName, dType, depth) => "Custom min error message"
    }
  },
}
```

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