Is

Returns the matching content type, if the incoming request’s Content-Type HTTP header field matches the MIME type specified by the type parameter.

If the request has no body, it returns false. 
  1. func (c *Ctx) Is(extension string) bool
  1. // Content-Type: text/html; charset=utf-8
  3. app.Get("/", func(c *fiber.Ctx) error {
  4.   c.Is("html")  // true
  5.   c.Is(".html") // true
  6.   c.Is("json")  // false
  8.   // ...
  9. })