XMLHttpRequest: getResponseHeader() method

The XMLHttpRequest method getResponseHeader() returns the string containing the text of a particular header's value.

If there are multiple response headers with the same name, then their values are returned as a single concatenated string, where each value is separated from the previous one by a pair of comma and space. The getResponseHeader() method returns the value as a UTF byte sequence.

If you need to get the raw string of all of the headers, use the getAllResponseHeaders() method, which returns the entire raw header string.

Syntax

getResponseHeader(headerName)

Parameters

headerName

A string indicating the name of the header you want to return the text value of.

Return value

A string representing the header's text value, or null if either the response has not yet been received or the header doesn't exist in the response.

Examples

In this example, a request is created and sent, and a readystatechange handler is established to look for the readyState to indicate that the headers have been received; when that is the case, the value of the Content-Type header is fetched. If the Content-Type isn't the desired value, the XMLHttpRequest is canceled by calling abort().

const client = new XMLHttpRequest();
client.open("GET", "unicorns-are-awesome.txt", true);
client.send();

client.onreadystatechange = () => {
  if (client.readyState === client.HEADERS_RECEIVED) {
    const contentType = client.getResponseHeader("Content-Type");
    if (contentType !== my_expected_type) {
      client.abort();
    }
  }
};

Specifications

Browser compatibility

See also

• Using XMLHttpRequest
• HTTP headers
• getAllResponseHeaders()
• response
• Setting request headers: setRequestHeader()