The
XMLHttpRequest
method
setRequestHeader()
sets the value of an HTTP request header.
When using
setRequestHeader()
, you must call it after calling
open()
, but before calling
send()
.
If this method is called several times with the same header, the values are merged into one single request header.
Each time you call
setRequestHeader()
after the first time you call it, the specified text is appended to the end of the existing header's content.
If no
Accept
header has been set using this, an
Accept
header with the type
"*/*"
is sent with the request when
send()
is called.
For security reasons, there are several
forbidden request headers
whose values are controlled by the user agent. Any attempt to set a value for one of those headers from frontend JavaScript code will be ignored without warning or error.
In addition, the
Authorization
HTTP header may be added to a request, but will be removed if the request is redirected cross-origin.
Note:
For your custom fields, you may encounter a "
not allowed by Access-Control-Allow-Headers in preflight response
" exception when you send requests across domains.
In this situation, you need to set up the
Access-Control-Allow-Headers
in your response header at server side.
