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Gin Web Framework

JSONP

JSONP (JSON with Padding) is a technique for making cross-domain requests from browsers that predate CORS support. It works by wrapping a JSON response in a JavaScript function call. The browser loads the response via a <script> tag, which is not subject to the same-origin policy, and the wrapping function executes with the data as its argument.

When you call c.JSONP(), Gin checks for a callback query parameter. If present, the response body is wrapped as callbackName({"foo":"bar"}) with a Content-Type of application/javascript. If no callback is provided, the response behaves like a standard c.JSON() call.

package main


import (
  "net/http"


  "github.com/gin-gonic/gin"
)


func main() {
  router := gin.Default()


  router.GET("/JSONP", func(c *gin.Context) {
    data := map[string]interface{}{
      "foo": "bar",
    }


    // The callback name is read from the query string, e.g.:
    // GET /JSONP?callback=x
    // Will output  :   x({\"foo\":\"bar\"})
    c.JSONP(http.StatusOK, data)
  })


  // Listen and serve on 0.0.0.0:8080
  router.Run(":8080")
}

Test with curl to see the difference between JSONP and plain JSON responses:

Terminal window
# With callback -- returns JavaScript
curl "http://localhost:8080/JSONP?callback=handleData"
# Output: handleData({"foo":"bar"});


# Without callback -- returns plain JSON
curl "http://localhost:8080/JSONP"
# Output: {"foo":"bar"}

See also