Get html header javascript

Response: headers property

The headers read-only property of the Response interface contains the Headers object associated with the response.

Value

Examples

In our Fetch Response example (see Fetch Response live) we create a new Request object using the Request() constructor, passing it a JPG path. We then fetch this request using fetch() , extract a blob from the response using Response.blob , create an object URL out of it using URL.createObjectURL , and display this in an .

Note that at the top of the fetch() block, we log the response headers to the console.

const myImage = document.querySelector("img"); const myRequest = new Request("flowers.jpg"); fetch(myRequest).then((response) =>  // for each response header, log an array with header name as key console.log(. response.headers); response.blob().then((myBlob) =>  const objectURL = URL.createObjectURL(myBlob); myImage.src = objectURL; >); >); 

Specifications

Browser compatibility

BCD tables only load in the browser

See also

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Headers

The Headers interface of the Fetch API allows you to perform various actions on HTTP request and response headers. These actions include retrieving, setting, adding to, and removing headers from the list of the request’s headers.

A Headers object has an associated header list, which is initially empty and consists of zero or more name and value pairs. You can add to this using methods like append() (see Examples.) In all methods of this interface, header names are matched by case-insensitive byte sequence.

For security reasons, some headers can only be controlled by the user agent. These headers include the forbidden header names and forbidden response header names.

A Headers object also has an associated guard, which takes a value of immutable , request , request-no-cors , response , or none . This affects whether the set() , delete() , and append() methods will mutate the header. For more information see Guard.

You can retrieve a Headers object via the Request.headers and Response.headers properties, and create a new Headers object using the Headers() constructor.

An object implementing Headers can directly be used in a for. of structure, instead of entries() : for (const p of myHeaders) is equivalent to for (const p of myHeaders.entries()) .

Note: you can find out more about the available headers by reading our HTTP headers reference.

Constructor

Creates a new Headers object.

Instance methods

Appends a new value onto an existing header inside a Headers object, or adds the header if it does not already exist.

Deletes a header from a Headers object.

Returns an iterator allowing to go through all key/value pairs contained in this object.

Executes a provided function once for each key/value pair in this Headers object.

Returns a String sequence of all the values of a header within a Headers object with a given name.

Returns an array containing the values of all Set-Cookie headers associated with a response.

Returns a boolean stating whether a Headers object contains a certain header.

Returns an iterator allowing you to go through all keys of the key/value pairs contained in this object.

Sets a new value for an existing header inside a Headers object, or adds the header if it does not already exist.

Returns an iterator allowing you to go through all values of the key/value pairs contained in this object.

Note: To be clear, the difference between Headers.set() and Headers.append() is that if the specified header does already exist and does accept multiple values, Headers.set() will overwrite the existing value with the new one, whereas Headers.append() will append the new value onto the end of the set of values. See their dedicated pages for example code.

Note: All of the Headers methods will throw a TypeError if you try to pass in a reference to a name that isn’t a valid HTTP Header name. The mutation operations will throw a TypeError if the header has an immutable Guard. In any other failure case they fail silently.

Note: When Header values are iterated over, they are automatically sorted in lexicographical order, and values from duplicate header names are combined.

Examples

In the following snippet, we create a new header using the Headers() constructor, add a new header to it using append() , then return that header value using get() :

const myHeaders = new Headers(); myHeaders.append("Content-Type", "text/xml"); myHeaders.get("Content-Type"); // should return 'text/xml' 

The same can be achieved by passing an array of arrays or an object literal to the constructor:

let myHeaders = new Headers( "Content-Type": "text/xml", >); // or, using an array of arrays: myHeaders = new Headers([["Content-Type", "text/xml"]]); myHeaders.get("Content-Type"); // should return 'text/xml' 

Specifications

Browser compatibility

BCD tables only load in the browser

See also

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Как отправить или получить HTTP заголовки на JavaScript

05.12.18 ИТ / JavaScript 13817

Обычно для работы с заголовками используется серверный язык, однако можно попробовать использовать и JavaScript (JS).

Как отправить HTTP заголовки запроса

Отправить заголовки на JavaScript можно при помощи Ajax-запросов. На чистом языке без применения библиотек это может выглядеть так:

var request = new XMLHttpRequest(); request.open('GET', document.location, false); request.setRequestHeader('Accept', 'text/plain'); request.setRequestHeader('Content-Type', 'text/plain'); request.setRequestHeader('Content-Language', 'en-US'); request.send(null); request.getAllResponseHeaders().toLowerCase();

Как получить HTTP заголовки ответа

Получить заголовки на JavaScript задача посложней, так как это язык работает на стороне клиента. Но можно отправить запрос на сервер средствами Ajax и получить примерно похожие заголовки при помощи функции getAllResponseHeaders. Примерный код:

var request = new XMLHttpRequest(); request.open('GET', document.location, false); request.send(null); request.getAllResponseHeaders().toLowerCase();

Таким образом, отправить или получить заголовки можно и при помощи языка JavaScript, а не только при помощи серверных языков, наподобие PHP.

Источник

Request: headers property

The headers read-only property of the Request interface contains the Headers object associated with the request.

Value

Examples

In the following snippet, we create a new request using the Request() constructor (for an image file in the same directory as the script), then save the request headers in a variable:

const myRequest = new Request("flowers.jpg"); const myHeaders = myRequest.headers; // Headers <> 

To add a header to the Headers object we use Headers.append ; we then create a new Request along with a 2nd init parameter, passing headers in as an init option:

const myHeaders = new Headers(); myHeaders.append("Content-Type", "image/jpeg"); const myInit =  method: "GET", headers: myHeaders, mode: "cors", cache: "default", >; const myRequest = new Request("flowers.jpg", myInit); const myContentType = myRequest.headers.get("Content-Type"); // returns 'image/jpeg' 

Specifications

Browser compatibility

BCD tables only load in the browser

See also

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Headers: get() method

The get() method of the Headers interface returns a byte string of all the values of a header within a Headers object with a given name. If the requested header doesn’t exist in the Headers object, it returns null .

For security reasons, some headers can only be controlled by the user agent. These headers include the forbidden header names and forbidden response header names.

Syntax

Parameters

The name of the HTTP header whose values you want to retrieve from the Headers object. If the given name is not the name of an HTTP header, this method throws a TypeError . The name is case-insensitive.

Return value

A String sequence representing the values of the retrieved header or null if this header is not set.

Examples

Creating an empty Headers object is simple:

const myHeaders = new Headers(); // Currently empty myHeaders.get("Not-Set"); // Returns null 

You could add a header to this using Headers.append , then retrieve it using get() :

.append("Content-Type", "image/jpeg"); myHeaders.get("Content-Type"); // Returns "image/jpeg" 

If the header has multiple values associated with it, the byte string will contain all the values, in the order they were added to the Headers object:

.append("Accept-Encoding", "deflate"); myHeaders.append("Accept-Encoding", "gzip"); myHeaders.get("Accept-Encoding"); // Returns "deflate, gzip" myHeaders .get("Accept-Encoding") .split(",") .map((v) => v.trimStart()); // Returns [ "deflate", "gzip" ] 

Specifications

Browser compatibility

BCD tables only load in the browser

See also

Found a content problem with this page?

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