GitBook: [master] one page modified

Author: christianalfoni

untitled.md

@@ -1,2 +1,76 @@
 # Side effects
 
+Overmind helps you expose side effects to your application logic. It does this with a concept called **Providers**. A provider is nothing more than an object with methods or a class instance. For example exposing an http library like [axios](https://github.com/axios/axios)  could be done like this:
+
+{% code-tabs %}
+{% code-tabs-item title="app/providers.js" %}
+```javascript
+export { default as axios } from 'axios'
+```
+{% endcode-tabs-item %}
+{% endcode-tabs %}
+
+Or you could expose it as a class and create a custom **API**:
+
+```javascript
+import axios from 'axios'
+
+class Api {
+  constructor (baseUrl) {
+    this.baseUrl = baseUrl
+  }
+  get(url, ...args) {
+    return axios.get(this.baseUrl + url, ...args)
+  }
+}
+
+export const api = new Api('/api/v1')
+```
+
+Using a class is useful when you want to pass in options based on the environment, or maybe the library exposes a class in itself.
+
+The providers are added to the configuration of the app:
+
+{% code-tabs %}
+{% code-tabs-item title="app/index.js" %}
+```javascript
+import App from 'overmind/$VIEW'
+import state from './state'
+import actions from './actions'
+import providers from './providers'
+
+const app = new App({
+  state,
+  actions,
+  providers
+})
+
+export const connect = app.connect
+```
+{% endcode-tabs-item %}
+
+{% code-tabs-item title="app/index.ts" %}
+```typescript
+import App, { TContext, IAction, TConnect } from 'overmind/$VIEW'
+import state from './state'
+import actions from './actions'
+import providers from './providers'
+
+export type Context = TContext<typeof state, typeof providers>
+
+export type Action = IAction<typeof state, Context>
+
+const app = new App({
+  state,
+  actions
+})
+
+export type Connect = TConnect<typeof app.state, typeof app.actions>
+
+export const connect = app.connect
+```
+{% endcode-tabs-item %}
+{% endcode-tabs %}
+
+The Overmind devtools will actually track any usage of these providers and give you valuable information about their execution.
+