Extract a cookie value

Read a named cookie from the request header in a function and use its value to shape the response you return.

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Read the value of a specific cookie by name directly on Azion’s global network and use it to shape the response. This is helpful for A/B testing, personalization, or any logic that depends on data your application already stores in the visitor’s cookies.

JavaScript
01const COOKIE_NAME = "hubspotutk"
02
03function getCookie(request, name) {
04 let result = ""
05 const cookieString = request.headers.get("Cookie")
06 if (cookieString) {
07 const cookies = cookieString.split(";")
08 cookies.forEach(cookie => {
09 const cookiePair = cookie.split("=", 2)
10 const cookieName = cookiePair[0].trim()
11 if (cookieName === name) {
12 const cookieVal = cookiePair[1]
13 result = cookieVal
14 }
15 })
16 }
17 return result
18}
19
20function handleRequest(request) {
21 const cookie = getCookie(request, COOKIE_NAME)
22 if (cookie) {
23 return new Response(cookie)
24 }
25 return new Response("No cookie with name: " + COOKIE_NAME)
26}
27
28addEventListener("fetch", event => {
29 event.respondWith(handleRequest(event.request))
30})

How it works

The helper getCookie reads the Cookie header with request.headers.get("Cookie"), splits it on ; into individual pairs, and splits each pair on = to compare the cookie name against the one you want. When a match is found, it returns that cookie’s value. The fetch handler then calls getCookie and uses event.respondWith() with a new Response, returning either the cookie value or a message noting the cookie was not present.

JavaScript examples

Browse the other ready-to-use examples you can copy into a function.

FetchEvent

Reference for the fetch event and the request the handler receives.

Request

Reference for the request object whose Cookie header this example reads.

Quickstart

What an account needs before a function can run, and the steps that put one in the path of a request.

Query usage data from Functions

Read back the compute time and the invocations this function has consumed.