# Use Executor Configurations

The `configurations` property provides extra sets of values that will be merged into the options map.

```json
{
  "build": {
    "executor": "@nrwl/js:tsc",
    "outputs": ["dist/libs/mylib"],
    "dependsOn": ["^build"],
    "options": {
      "tsConfig": "libs/mylib/tsconfig.lib.json",
      "main": "libs/mylib/src/main.ts"
    },
    "configurations": {
      "production": {
        "tsConfig": "libs/mylib/tsconfig-prod.lib.json"
      }
    }
  }
}
```

You can select a configuration like this: `nx build mylib --configuration=production`
or `nx run mylib:build:configuration=production`.

The following code snippet shows how the executor options get constructed:

```javascript
require(`@nrwl/jest`).executors['jest']({
  ...options,
  ...selectedConfiguration,
  ...commandLineArgs,
}); // Pseudocode
```

The selected configuration adds/overrides the default options, and the provided command line args add/override the
configuration options.