## JSONP
JSONP 是一个能够被跨域访问资源的方法。
#### 服务端
`server.go`
```go
package main
import (
"math/rand"
"net/http"
"time"
"github.com/labstack/echo"
"github.com/labstack/echo/middleware"
)
func main() {
e := echo.New()
e.Use(middleware.Logger())
e.Use(middleware.Recover())
e.Static("/", "public")
// JSONP
e.GET("/jsonp", func(c echo.Context) error {
callback := c.QueryParam("callback")
var content struct {
Response string `json:"response"`
Timestamp time.Time `json:"timestamp"`
Random int `json:"random"`
}
content.Response = "Sent via JSONP"
content.Timestamp = time.Now().UTC()
content.Random = rand.Intn(1000)
return c.JSONP(http.StatusOK, callback, &content)
})
// Start server
e.Logger.Fatal(e.Start(":1323"))
}
```
### 客户端
`index.html`
```html
<!DOCTYPE html>
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8" />
<link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.5/css/bootstrap.min.css">
<title>JSONP</title>
<script type="text/javascript" src="//ajax.googleapis.com/ajax/libs/jquery/1/jquery.min.js"></script>
<script type="text/javascript">
var host_prefix = 'http://localhost:1323';
$(document).ready(function() {
// JSONP version - add 'callback=?' to the URL - fetch the JSONP response to the request
$("#jsonp-button").click(function(e) {
e.preventDefault();
// The only difference on the client end is the addition of 'callback=?' to the URL
var url = host_prefix + '/jsonp?callback=?';
$.getJSON(url, function(jsonp) {
console.log(jsonp);
$("#jsonp-response").html(JSON.stringify(jsonp, null, 2));
});
});
});
</script>
</head>
<body>
<div class="container" style="margin-top: 50px;">
<input type="button" class="btn btn-primary btn-lg" id="jsonp-button" value="Get JSONP response">
<p>
<pre id="jsonp-response"></pre>
</p>
</div>
</body>
</html>
```
