Creating WebUI Interfaces

A WebUI page is made of a Polymer single-page application, which communicates with a C++ UI controller, as explained here.

WebUI pages live in chrome/browser/resources and their native counterpart in chrome/browser/ui/webui/. We will start by creating folders for the new page in chrome/browser/[resources|ui/webui]/hello_world. When creating WebUI resources, follow the Web Development Style Guide.

Making a basic WebUI page

For a sample WebUI page you could start with the following files:

chrome/browser/resources/hello_world/hello_world.html

<!DOCTYPE HTML>
<html>
  <meta charset="utf-8">
  <link rel="stylesheet" href="hello_world.css">
  <hello-world-app></hello-world-app>
  <script type="module" src="app.js"></script>
</html>

chrome/browser/resources/hello_world/hello_world.css

body {
  margin: 0;
}

chrome/browser/resources/hello_world/app.html

<h1>Hello World</h1>
<div id="example-div">[[message_]]</div>

chrome/browser/resources/hello_world/app.ts

import './strings.m.js';

import {loadTimeData} from 'chrome://resources/js/load_time_data.js';
import {PolymerElement} from 'chrome://resources/polymer/v3_0/polymer/polymer_bundled.min.js';
import {getTemplate} from './app.html.js';

export class HelloWorldAppElement extends PolymerElement {
  static get is() {
    return 'hello-world-app';
  }

  static get template() {
    return getTemplate();
  }

  static get properties() {
    return {
      message_: {
        type: String,
        value: () => loadTimeData.getString('message'),
      },
    };
  }
}

declare global {
  interface HTMLElementTagNameMap {
    'hello-world-app': HelloWorldAppElement;
  }
}

customElements.define(HelloWorldAppElement.is, HelloWorldAppElement);

Add a tsconfig_base.json file to configure TypeScript options. Typical options needed by Polymer UIs include:

disabling noUncheckedIndexAccess
disabling noUnusedLocals: private members from Elements are accessed from their HTML template
disabling strictPropertyInitialization: Element properties can be initialized via the property map.

chrome/browser/resources/hello_world/tsconfig_base.json

{
  "extends": "../../../../tools/typescript/tsconfig_base.json",
  "compilerOptions": {
    "noUncheckedIndexedAccess": false,
    "noUnusedLocals": false,
    "strictPropertyInitialization": false
  }
}

Add a BUILD.gn file to get TypeScript compilation and to generate the JS file from which the template will be imported.

chrome/browser/resources/hello_world/BUILD.gn

import("//ui/webui/resources/tools/build_webui.gni")

build_webui("build") {
  grd_prefix = "hello_world"

  static_files = [ "hello_world.html", "hello_world.css" ]

  web_component_files = [ "app.ts" ]

  non_web_component_files = [
    # For example the BrowserProxy file would go here.
  ]

  ts_deps = [
    "//third_party/polymer/v3_0:library",
    "//ui/webui/resources/js:build_ts",
  ]
}

Note: See the build config docs for more examples of how the build could be configured.

Finally, create an OWNERS file for the new folder.

Adding the resources

The build_webui target in BUILD.gn autogenerates some targets and files that need to be linked from the binary-wide resource targets:

Add the new resource target to chrome/browser/resources/BUILD.gn

group("resources") {
  public_deps += [
    ...
    "hello_world:resources"
    ...
  ]
}

Add an entry to resource_ids.spec

This file is for automatically generating resource ids. Ensure that your entry has a unique ID and preserves numerical ordering. If you see an error like “ValueError: Cannot jump to unvisited”, please check the numeric order of your resource ids.

tools/gritsettings/resource_ids.spec

  # START chrome/ WebUI resources section
  ... (lots)
  "<(SHARED_INTERMEDIATE_DIR)/chrome/browser/resources/hello_world/resources.grd": {
    "META": {"sizes": {"includes": [5]}},
    "includes": [2085],
  },

Also add to chrome/chrome_paks.gni

template("chrome_extra_paks") {
  ... (lots)
  sources += [
    ...
    "$root_gen_dir/chrome/hello_world_resources.pak",
    ...
  ]
  deps += [
    ...
    "//chrome/browser/resources/hello_world:resources",
    ...
  ]
}

Adding URL constants for the new chrome URL

chrome/common/webui_url_constants.cc:

const char kChromeUIHelloWorldURL[] = "chrome://hello-world/";
const char kChromeUIHelloWorldHost[] = "hello-world";

chrome/common/webui_url_constants.h:

extern const char kChromeUIHelloWorldURL[];
extern const char kChromeUIHelloWorldHost[];

Adding a WebUI class for handling requests to the `chrome://hello-world/` URL

Next we need a class to handle requests to this new resource URL. Typically this will subclass WebUIController (WebUI dialogs will also need another class which will subclass WebDialogDelegate, this is shown later).

chrome/browser/ui/webui/hello_world/hello_world_ui.h

#ifndef CHROME_BROWSER_UI_WEBUI_HELLO_WORLD_HELLO_WORLD_H_
#define CHROME_BROWSER_UI_WEBUI_HELLO_WORLD_HELLO_WORLD_H_

#include "content/public/browser/web_ui_controller.h"

// The WebUI for chrome://hello-world
class HelloWorldUI : public content::WebUIController {
 public:
  explicit HelloWorldUI(content::WebUI* web_ui);
  ~HelloWorldUI() override;
};

#endif // CHROME_BROWSER_UI_WEBUI_HELLO_WORLD_HELLO_WORLD_H_

chrome/browser/ui/webui/hello_world/hello_world_ui.cc

#include "chrome/browser/ui/webui/hello_world/hello_world_ui.h"

#include "chrome/browser/ui/webui/webui_util.h"
#include "chrome/common/webui_url_constants.h"
#include "content/public/browser/browser_context.h"
#include "content/public/browser/web_contents.h"
#include "chrome/grit/hello_world_resources.h"
#include "chrome/grit/hello_world_resources_map.h"
#include "content/public/browser/web_ui.h"
#include "content/public/browser/web_ui_data_source.h"


HelloWorldUI::HelloWorldUI(content::WebUI* web_ui)
    : content::WebUIController(web_ui) {
  // Set up the chrome://hello-world source.
  content::WebUIDataSource* source = content::WebUIDataSource::CreateAndAdd(
      web_ui->GetWebContents()->GetBrowserContext(),
      chrome::kChromeUIHelloWorldHost);

  // Add required resources.
  webui::SetupWebUIDataSource(
      source,
      base::make_span(kHelloWorldResources, kHelloWorldResourcesSize),
      IDR_HELLO_WORLD_HELLO_WORLD_HTML);

  // As a demonstration of passing a variable for JS to use we pass in some
  // a simple message.
  source->AddString("message", "Hello World!");
}

HelloWorldUI::~HelloWorldUI() = default;

To ensure that your code actually gets compiled, you need to add it to chrome/browser/ui/BUILD.gn:

static_library("ui") {
  sources = [
    ... (lots)
    "webui/hello_world/hello_world_ui.cc",
    "webui/hello_world/hello_world_ui.h",
    ...
  ]
}

Preferred method: Add a WebUIConfig class and put it in the WebUIConfigMap

WebUIConfigs contain minimal information about the host and scheme served by the WebUIController subclass. It also can enable or disable the UI for different conditions (e.g. feature flag status). You can create a WebUIConfig subclass and register it in the WebUIConfigMap to ensure your request handler is instantiated and used to handle any requests to the desired scheme + host.

chrome/browser/ui/webui/hello_world/hello_world_ui.h

class HelloWorldUIConfig : public content::WebUIConfig {
 public:
  HelloWorldUIConfig();
  ~HelloWorldUIConfig() override;

  // content::WebUIConfig:
  std::unique_ptr<content::WebUIController> CreateWebUIController(
      content::WebUI* web_ui,
      const GURL& url) override;
};

chrome/browser/ui/webui/hello_world/hello_world_ui.cc

HelloWorldUIConfig::HelloWorldUIConfig()
    : WebUIConfig(content::kChromeUIScheme, chrome::kChromeUIHelloWorldHost) {}

HelloWorldUIConfig::~HelloWorldUIConfig() = default;

std::unique_ptr<content::WebUIController>
HelloWorldUIConfig::CreateWebUIController(content::WebUI* web_ui,
                                         const GURL& url) {
  return std::make_unique<HelloWorldUI>(web_ui);
}

Register your config in chrome_web_ui_configs.cc, for trusted UIs, or chrome_untrusted_web_ui_configs.cc for untrusted UIs.

chrome/browser/ui/webui/chrome_web_ui_configs.cc

+ #include "chrome/browser/ui/webui/hello_world/hello_world_ui.h"
...
+map.AddWebUIConfig(std::make_unique<hello_world::HelloWorldUIConfig>());

Old method: Add your WebUI request handler to the Chrome WebUI factory

The Chrome WebUI factory is another way to setup your new request handler. This is how many older WebUIs in Chrome are registered, since not all UIs have been migrated to use the newer WebUIConfig (see migration bug). Only use this method for a new UI if the approach above using WebUIConfig does not work, and notify WebUI PLATFORM_OWNERS.

chrome/browser/ui/webui/chrome_web_ui_controller_factory.cc:

+ #include "chrome/browser/ui/webui/hello_world/hello_world_ui.h"
...
+ if (url.host() == chrome::kChromeUIHelloWorldHost)
+   return &NewWebUI<HelloWorldUI>;

Check everything works

You're done! Assuming no errors (because everyone gets their code perfect the first time) you should be able to compile and run chrome and navigate to chrome://hello-world/ and see your nifty welcome text!

Making a WebUI Dialog

Instead of having a full page for your WebUI, you might want a dialog in order to have a fully independent window. To do that, some small changes are needed to your code. First, we need to add a new class which inherits from ui::WebDialogDelegate. The easiest way to do that is to edit the hello_world_ui.* files

chrome/browser/ui/webui/hello_world/hello_world_ui.h

 // Leave the old content, but add this new code
 class HelloWorldDialog : public ui::WebDialogDelegate {
 public:
  static void Show();
  ~HelloWorldDialog() override;
  HelloWorldDialog(const HelloWorldDialog&) = delete;
  HelloWorldDialog& operator=(const HelloWorldDialog&) = delete;

 private:
  HelloWorldDialog();
  // ui::WebDialogDelegate:
  ui::ModalType GetDialogModalType() const override;
  std::u16string GetDialogTitle() const override;
  GURL GetDialogContentURL() const override;
  void GetWebUIMessageHandlers(
      std::vector<content::WebUIMessageHandler*>* handlers) const override;
  void GetDialogSize(gfx::Size* size) const override;
  std::string GetDialogArgs() const override;
  void OnDialogShown(content::WebUI* webui) override;
  void OnDialogClosed(const std::string& json_retval) override;
  void OnCloseContents(content::WebContents* source,
                       bool* out_close_dialog) override;
  bool ShouldShowDialogTitle() const override;

  content::WebUI* webui_ = nullptr;
};

chrome/browser/ui/webui/hello_world/hello_world_ui.cc

 // Leave the old content, but add this new stuff

HelloWorldDialog::HelloWorldDialog() = default;

void HelloWorldDialog::Show() {
  // HelloWorldDialog is self-deleting via OnDialogClosed().
  chrome::ShowWebDialog(nullptr, ProfileManager::GetActiveUserProfile(),
                        new HelloWorldDialog());
}

ui::ModalType HelloWorldDialog::GetDialogModalType() const {
  return ui::MODAL_TYPE_NONE;
}

std::u16string HelloWorldDialog::GetDialogTitle() const {
  return u"Hello world";
}

GURL HelloWorldDialog::GetDialogContentURL() const {
  return GURL(chrome::kChromeUIHelloWorldURL[);
}

void HelloWorldDialog::GetWebUIMessageHandlers(
    std::vector<content::WebUIMessageHandler*>* handlers) const {}

void HelloWorldDialog::GetDialogSize(gfx::Size* size) const {
  const int kDefaultWidth = 544;
  const int kDefaultHeight = 628;
  size->SetSize(kDefaultWidth, kDefaultHeight);
}

std::string HelloWorldDialog::GetDialogArgs() const {
  return "";
}

void HelloWorldDialog::OnDialogShown(content::WebUI* webui) {
  webui_ = webui;
}

void HelloWorldDialog::OnDialogClosed(const std::string& json_retval) {
  delete this;
}

void HelloWorldDialog::OnCloseContents(content::WebContents* source,
                                        bool* out_close_dialog) {
  *out_close_dialog = true;
}

bool HelloWorldDialog::ShouldShowDialogTitle() const {
  return true;
}

HelloWorldDialog::~HelloWorldDialog() = default;

Finally, you will need to do something to actually show your dialog, which can be done by calling HelloWorldDialog::Show().

More elaborate configurations

Referencing resources from another webui page

There are already mechanisms to make resources available chrome-wide, by publishing them under chrome://resources. If this is not appropriate, there are some ways to serve a file from some other webui page directly through another host.

First, a few explanations. The configuration based on the build_webui() BUILD target as presented above generates a few helpers that hide the complexity of the page's configuration. For example, considering the snippet below:

//...
#include "chrome/grit/hello_world_resources.h"
#include "chrome/grit/hello_world_resources_map.h"

HelloWorldUI::HelloWorldUI(content::WebUI* web_ui)
    : content::WebUIController(web_ui) {
  // ...
  webui::SetupWebUIDataSource(
      source,
      base::make_span(kHelloWorldResources, kHelloWorldResourcesSize),
      IDR_HELLO_WORLD_HELLO_WORLD_CONTAINER_HTML);
}

kHelloWorldResources and kHelloWorldResourcesSize come from from the imported grit-generated files, as configured by the build target, and reference the files listed in it so they can be served out of the given host name. For example, they would contain values like:

const webui::ResourcePath kHelloWorldResources[] = {
  {"hello_world.html", IDR_CHROME_BROWSER_RESOURCES_HELLO_WORLD_HELLO_WORLD_HTML},
  {"hello_world.css", IDR_CHROME_BROWSER_RESOURCES_HELLO_WORLD_HELLO_WORLD_CSS},
};

Using WebUIDataSource::AddResourcePaths() we can add other resources, looking for the right way to declare them by looking through the generated grit files (e.g. via codesearch), or manual registrations if they exist.

#include "chrome/grit/signin_resources.h"
// ...
HelloWorldUI::HelloWorldUI(content::WebUI* web_ui) {
  // ...
  static constexpr webui::ResourcePath kResources[] = {
      {"signin_shared.css.js", IDR_SIGNIN_SIGNIN_SHARED_CSS_JS},
      {"signin_vars.css.js", IDR_SIGNIN_SIGNIN_VARS_CSS_JS},
  };
  source->AddResourcePaths(kResources);
}

Creating WebUI Interfaces

Making a basic WebUI page

Adding the resources

Adding URL constants for the new chrome URL

Adding a WebUI class for handling requests to the chrome://hello-world/ URL

Preferred method: Add a WebUIConfig class and put it in the WebUIConfigMap

Old method: Add your WebUI request handler to the Chrome WebUI factory

Check everything works

Making a WebUI Dialog

More elaborate configurations

Referencing resources from another webui page

Adding a WebUI class for handling requests to the `chrome://hello-world/` URL