Add support to stringify automatically the body of the request if the type of it isn't a string

This allows us the make the request sending a javascript object and then RequestJS does the job of stringify the body

Author: marcelolx

README.md

@@ -54,6 +54,23 @@ async myMethod () {
 }
 ```
 
+#### Request body
+
+Instead of stringify the body of a request which the content type is `application/json`, you can just pass the javascript object as the body of the request and Request.JS will stringify it for you.
+
+```js
+import { post } from '@rails/request.js'
+
+...
+
+async myMethod () {
+  const response = await post('localhost:3000/my_endpoint', { body: { name: 'Request.JS' } })
+  if (response.ok) {
+    ...
+  }
+}
+```
+
 
 #### Turbo Streams
 

src/fetch_request.js

@@ -24,7 +24,10 @@ export class FetchRequest {
       return Promise.reject(window.location.href = response.authenticationURL)
     }
 
-    if (response.ok && response.isTurboStream) { response.renderTurboStream() }
+    if (response.ok && response.isTurboStream) {
+      response.renderTurboStream()
+    }
+
     return response
   }
 
@@ -35,14 +38,18 @@ export class FetchRequest {
   }
 
   get fetchOptions () {
-    return {
+    const requestOptions = {
       method: this.method.toUpperCase(),
       headers: this.headers,
       body: this.body,
       signal: this.signal,
       credentials: 'same-origin',
       redirect: 'follow'
     }
+
+    this._stringifyBody(requestOptions)
+
+    return requestOptions
   }
 
   get headers () {
@@ -101,4 +108,13 @@ export class FetchRequest {
   get additionalHeaders () {
     return this.options.headers || {}
   }
+
+  _stringifyBody (requestOptions) {
+    const bodyIsAString = Object.prototype.toString.call(requestOptions.body) === '[object String]'
+    const contentTypeIsJson = requestOptions.headers['Content-Type'] === 'application/json'
+
+    if (contentTypeIsJson && !bodyIsAString) {
+      requestOptions.body = JSON.stringify(requestOptions.body)
+    }
+  }
 }