Proxy – JavaScript – MDN Web Docs
200) {
throw new RangeError(‘The age seems invalid’);}}
// The default behavior to store the value
obj[prop] = value;
// Indicate success
return true;}};
const person = new Proxy({}, validator);
= 100;
(); // 100
= ‘young’; // Throws an exception
= 300; // Throws an exception
Extending constructorA function proxy could easily extend a constructor with a new constructor. This example uses the construct() and apply() handlers.
function extend(sup, base) {
var descriptor = tOwnPropertyDescriptor(
ototype, ‘constructor’);
ototype = (ototype);
var handler = {
construct: function(target, args) {
var obj = (ototype);
(target, obj, args);
return obj;},
apply: function(target, that, args) {
(that, args);
(that, args);}};
var proxy = new Proxy(base, handler);
= proxy;
fineProperty(ototype, ‘constructor’, descriptor);
return proxy;}
var Person = function(name) {
= name;};
var Boy = extend(Person, function(name, age) {
= age;});
= ‘M’;
var Peter = new Boy(‘Peter’, 13);
(); // “M”
(); // “Peter”
(); // 13
Manipulating DOM nodesSometimes you want to toggle the attribute or class name of two different elements. Here’s how using the set() handler.
let view = new Proxy({
selected: null},
{
set: function(obj, prop, newval) {
let oldval = obj[prop];
if (prop === ‘selected’) {
if (oldval) {
tAttribute(‘aria-selected’, ‘false’);}
if (newval) {
tAttribute(‘aria-selected’, ‘true’);}}
obj[prop] = newval;
return true;}});
let i1 = lected = tElementById(‘item-1’); //giving error here, i1 is null
(tAttribute(‘aria-selected’));
// ‘true’
let i2 = lected = tElementById(‘item-2’);
// ‘false’
Note: even if selected:! null, then giving tAttribute is not a function
Value correction and an extra propertyThe products proxy object evaluates the passed value and converts it to an array if needed. The object also supports an extra property called latestBrowser both as a getter and a setter.
let products = new Proxy({
browsers: [‘Internet Explorer’, ‘Netscape’]},
// An extra property
if (prop === ‘latestBrowser’) {
return owsers[ – 1];}
// The default behavior to return the value
return obj[prop];},
(value);
return true;}
// Convert the value if it is not an array
if (typeof value === ‘string’) {
value = [value];}
(owsers);
// [‘Internet Explorer’, ‘Netscape’]
owsers = ‘Firefox’;
// pass a string (by mistake)
// [‘Firefox’] <- no problem, the value is an array
testBrowser = 'Chrome';
// ['Firefox', 'Chrome']
(testBrowser);
// 'Chrome'
Finding an array item object by its propertyThis proxy extends an array with some utility features. As you see, you can flexibly "define" properties without using fineProperties(). This example can be adapted to find a table row by its cell. In that case, the target will be
let products = new Proxy([
{ name: 'Firefox', type: 'browser'},
{ name: 'SeaMonkey', type: 'browser'},
{ name: 'Thunderbird', type: 'mailer'}],
// The default behavior to return the value; prop is usually an integer
if (prop in obj) {
return obj[prop];}
// Get the number of products; an alias of
if (prop === 'number') {
return;}
let result, types = {};
for (let product of obj) {
if ( === prop) {
result = product;}
if (types[]) {
types[](product);} else {
types[] = [product];}}
// Get a product by name
if (result) {
return result;}
// Get products by type
if (prop in types) {
return types[prop];}
// Get product types
if (prop === 'types') {
return (types);}
return undefined;}});
(products[0]); // { name: 'Firefox', type: 'browser'}
(products['Firefox']); // { name: 'Firefox', type: 'browser'}
(products['Chrome']); // undefined
(owser); // [{ name: 'Firefox', type: 'browser'}, { name: 'SeaMonkey', type: 'browser'}]
(); // ['browser', 'mailer']
(); // 3
A complete traps list exampleNow in order to create a complete sample traps list, for didactic purposes, we will try to proxify a non-native object that is particularly suited to this type of operation: the docCookies global object created by a simple cookie framework.
/*
var docCookies =... get the "docCookies" object here:
*/
var docCookies = new Proxy(docCookies, {
get: function (oTarget, sKey) {
return oTarget[sKey] || tItem(sKey) || undefined;},
set: function (oTarget, sKey, vValue) {
if (sKey in oTarget) { return false;}
return tItem(sKey, vValue);},
deleteProperty: function (oTarget, sKey) {
if (! sKey in oTarget) { return false;}
return moveItem(sKey);},
enumerate: function (oTarget, sKey) {
return ();},
ownKeys: function (oTarget, sKey) {
has: function (oTarget, sKey) {
return sKey in oTarget || oTarget. hasItem(sKey);},
defineProperty: function (oTarget, sKey, oDesc) {
if (oDesc && 'value' in oDesc) { tItem(sKey, );}
return oTarget;},
getOwnPropertyDescriptor: function (oTarget, sKey) {
var vValue = tItem(sKey);
return vValue? {
value: vValue,
writable: true,
enumerable: true,
configurable: false}: undefined;}, });
/* Cookies test */
(_cookie1 = 'First value');
(tItem('my_cookie1'));
tItem('my_cookie1', 'Changed value');
(_cookie1);
SpecificationsSpecificationECMAScript Language Specification (ECMAScript)# sec-proxy-objectsBrowser compatibilityBCD tables only load in the browserSee also
"Proxies are awesome" Brendan Eich presentation at JSConf (slides)
Tutorial on proxies" alt="nodejs proxy class,nodejs proxy object,npm proxy,nodejs https proxy,nodejs express proxy,node http-proxy-middleware,nodejs reverse proxy,http-proxy-middleware" title="nodejs proxy class,nodejs proxy object,npm proxy,nodejs https proxy,nodejs express proxy,node http-proxy-middleware,nodejs reverse proxy,http-proxy-middleware" />
nodejs proxy class,nodejs proxy object,npm proxy,nodejs https proxy,nodejs express proxy,node http-proxy-middleware,nodejs reverse proxy,http-proxy-middleware
What is Node JS proxy?
node-http-proxy is an HTTP programmable proxying library that supports websockets. It is suitable for implementing components such as reverse proxies and load balancers.
How do I setup a proxy server express?
HTTP
// Create the HTTPS proxy server in front of a HTTP server
eateServer({
target: {
host: ‘localhost’,
port: 9009},
ssl: {
key: adFileSync(”, ‘utf8’),
cert: adFileSync(”, ‘utf8’)}})(8009);
HTTPS -> HTTPS
// Create the proxy server listening on port 443
cert: adFileSync(”, ‘utf8’)},
target: ‘localhost:9010’,
secure: true // Depends on your needs, could be false. })(443);
HTTP -> HTTPS (using a PKCS12 client certificate)
// Create an HTTP proxy server with an HTTPS target
eateProxyServer({
protocol: ‘:’,
host: ‘my-domain-name’,
port: 443,
pfx: adFileSync(‘path/to/certificate. p12’),
passphrase: ‘password’, },
changeOrigin: true, })(8000);
You can activate the websocket support for the proxy using ws:true in the options.
// Create a proxy server for websockets
target: ‘wslocalhost:9014’,
ws: true})(8014);
Also you can proxy the websocket requests just calling the ws(req, socket, head) method.
// Setup our server to proxy standard HTTP requests
var proxy = new eateProxyServer({
port: 9015}});
var proxyServer = eateServer(function (req, res) {
(req, res);});
// Listen to the `upgrade` event and proxy the
// WebSocket requests as well.
(‘upgrade’, function (req, socket, head) {
(req, socket, head);});
(8015);
eateProxyServer supports the following options:
target: url string to be parsed with the url module
forward: url string to be parsed with the url module
agent: object to be passed to (s). request (see Node’s agent and agent objects)
ssl: object to be passed to eateServer()
ws: true/false, if you want to proxy websockets
xfwd: true/false, adds x-forward headers
secure: true/false, if you want to verify the SSL Certs
toProxy: true/false, passes the absolute URL as the path (useful for proxying to proxies)
prependPath: true/false, Default: true – specify whether you want to prepend the target’s path to the proxy path
ignorePath: true/false, Default: false – specify whether you want to ignore the proxy path of the incoming request (note: you will have to append / manually if required).
localAddress: Local interface string to bind for outgoing connections
changeOrigin: true/false, Default: false – changes the origin of the host header to the target URL
preserveHeaderKeyCase: true/false, Default: false – specify whether you want to keep letter case of response header key
auth: Basic authentication i. e. ‘user:password’ to compute an Authorization header.
hostRewrite: rewrites the location hostname on (201/301/302/307/308) redirects.
autoRewrite: rewrites the location host/port on (201/301/302/307/308) redirects based on requested host/port. Default: false.
protocolRewrite: rewrites the location protocol on (201/301/302/307/308) redirects to ” or ”. Default: null.
cookieDomainRewrite: rewrites domain of set-cookie headers. Possible values:
false (default): disable cookie rewriting
String: new domain, for example cookieDomainRewrite: “”. To remove the domain, use cookieDomainRewrite: “”.
Object: mapping of domains to new domains, use “*” to match all domains.
For example keep one domain unchanged, rewrite one domain and remove other domains:
cookieDomainRewrite: {
“”: “”,
“*”: “”}
cookiePathRewrite: rewrites path of set-cookie headers. Possible values:
String: new path, for example cookiePathRewrite: “/newPath/”. To remove the path, use cookiePathRewrite: “”. To set path to root use cookiePathRewrite: “/”.
Object: mapping of paths to new paths, use “*” to match all paths.
For example, to keep one path unchanged, rewrite one path and remove other paths:
cookiePathRewrite: {
“/”: “/”,
headers: object with extra headers to be added to target requests.
proxyTimeout: timeout (in millis) for outgoing proxy requests
timeout: timeout (in millis) for incoming requests
followRedirects: true/false, Default: false – specify whether you want to follow redirects
selfHandleResponse true/false, if set to true, none of the webOutgoing passes are called and it’s your responsibility to appropriately return the response by listening and acting on the proxyRes event
buffer: stream of data to send as the request body. Maybe you have some middleware that consumes the request stream before proxying it on e. g. If you read the body of a request into a field called ‘req. rawbody’ you could restream this field in the buffer option:
‘use strict’;
const streamify = require(‘stream-array’);
const HttpProxy = require(‘-proxy’);
const proxy = new HttpProxy();
module. exports = (req, res, next) => {
target: ‘localhost:4003/’,
buffer: streamify(req. rawBody)}, next);};
NOTE:
and are optional.
and rward cannot both be missing
If you are using the method, the following options are also applicable:
error: The error event is emitted if the request to the target fail. We do not do any error handling of messages passed between client and proxy, and messages passed between proxy and target, so it is recommended that you listen on errors and handle them.
proxyReq: This event is emitted before the data is sent. It gives you a chance to alter the proxyReq request object. Applies to “web” connections
proxyReqWs: This event is emitted before the data is sent. Applies to “websocket” connections
proxyRes: This event is emitted if the request to the target got a response.
open: This event is emitted once the proxy websocket was created and piped into the target websocket.
close: This event is emitted once the proxy websocket was closed.
(DEPRECATED) proxySocket: Deprecated in favor of open.
// Error example
// Http Proxy Server with bad target
var proxy = eateServer({
target:’localhost:9005′});
(8005);
// Listen for the `error` event on `proxy`.
(‘error’, function (err, req, res) {
res. writeHead(500, {
‘Content-Type’: ‘text/plain’});
(‘Something went wrong. And we are reporting a custom error message. ‘);});
// Listen for the `proxyRes` event on `proxy`.
(‘proxyRes’, function (proxyRes, req, res) {
(‘RAW Response from the target’, ringify(proxyRes. headers, true, 2));});
// Listen for the `open` event on `proxy`.
(‘open’, function (proxySocket) {
// listen for messages coming FROM the target here
(‘data’, hybiParseAndLogMessage);});
// Listen for the `close` event on `proxy`.
(‘close’, function (res, socket, head) {
// view disconnected websocket connections
(‘Client disconnected’);});
When testing or running server within another program it may be necessary to close the proxy.
This will stop the proxy from accepting new connections.
port: 1337}});
();
If you want to handle your own response after receiving the proxyRes, you can do
so with selfHandleResponse. As you can see below, if you use this option, you
are able to intercept and read the proxyRes but you must also make sure to
reply to the res itself otherwise the original client will never receive any
data.
Modify response
var option = {
target: target,
selfHandleResponse: true};
var body = [];
(‘data’, function (chunk) {
(chunk);});
(‘end’, function () {
body = (body). toString();
(“res from proxied server:”, body);
(“my response to cli”);});});
(req, res, option);
A proxy table API is available through this add-on module, which lets you define a set of rules to translate matching routes to target routes that the reverse proxy will talk to.
Logo created by Diego Pasquali
Read carefully our Code Of Conduct
Search on Google/Github
If you can’t find anything, open an issue
If you feel comfortable about fixing the issue, fork the repo
Commit to your local branch (which must be different from master)
Submit your Pull Request (be sure to include tests and update documentation)
The MIT License (MIT)
Copyright (c) 2010 – 2016 Charlie Robbins, Jarrett Cruger & the Contributors.
Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the “Software”), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:
The above copyright notice and this permission notice shall be included in
all copies or substantial portions of the Software.
THE SOFTWARE IS PROVIDED “AS IS”, WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
THE SOFTWARE.” alt=”Setup proxy server with ExpressStep 1: Install express and request npm install express –save npm install request –save.Step 2: Create server.js var express = require(‘express’); … Step 3: Setup the route (replace API_KEY with your API key) app.get(‘/api’, function(req, res){ … Step 4: Setup the port app.listen(3000);” title=”Setup proxy server with ExpressStep 1: Install express and request npm install express –save npm install request –save.Step 2: Create server.js var express = require(‘express’); … Step 3: Setup the route (replace API_KEY with your API key) app.get(‘/api’, function(req, res){ … Step 4: Setup the port app.listen(3000);” />
Setup proxy server with ExpressStep 1: Install express and request npm install express –save npm install request –save.Step 2: Create server.js var express = require(‘express’); … Step 3: Setup the route (replace API_KEY with your API key) app.get(‘/api’, function(req, res){ … Step 4: Setup the port app.listen(3000);
What is a proxy object JS?
