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Simple POC for managing accounts in a browser extension and allowing the signing of extrinsics using these accounts. Also provides simple interface for compliant extensions for dapps.
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polkadotjs license npm beta maintainability

polkadot{.js} extension

A very simple scaffolding browser extension that injects a @polkadot/api Signer into a page, along with any associated accounts, allowing for use by any dapp. This is an extensible POC implementation of a Polkadot/Substrate browser signer.

As it stands, it does one thing: it only manages accounts and allows the signing of transactions with those accounts. It does not inject providers for use by dapps at this early point, nor does it perform wallet functions where it constructs and submits txs to the network.


interface screenshots

Development version

Steps to build the extension and view your changes in a browser:

  1. Build via yarn build or yarn watch
  2. Install the extension
  • Chrome:
    • go to chrome://extensions/
    • ensure you have the Development flag set
    • "Load unpacked" and point to packages/extension/build
    • if developing, after making changes - refresh the extension
  • Firefox:
    • go to about:debugging#addons
    • check "Enable add-on debugging"
    • click on "Load Temporary Add-on" and point to packages/extension/build/manifest.json
    • if developing, after making changes - reload the extension
  1. When visiting it will inject the extension

Once added, you can create an account (via a generated seed) or import via an existing seed. The apps UI, when loaded, will show these accounts as <account name> (extension)


The repo is split into a number of packages -

  • extension - All the injection and background processing logic (the main entry)
  • extension-ui - The UI components for the extension, to build up the popup
  • extension-dapp - A convenience wrapper to work with the injected objects, simplifying data extraction for any dapp that wishes to integrate the extension (or any extension that supports the interface)
  • extension-inject - A convience wrapper that allows extension developers to inject their extension for use by any dapp

Dapp developers

The actual in-depth technical breakdown is given in the next section for any dapp developer wishing to work with the raw objects injected into the window. However, convenience wrappers are provided that allows for any dapp to use this extension (or any other extension that conforms to the interface) without having to manage any additional info.

This approach is used to support multiple external signers in for instance apps. You can read more about the convenience wrapper @polkadot/extension-dapp along with usage samples.

API interface

The extension injection interfaces are generic, i.e. it is designed to allow any extension developer to easily inject extensions (that conforms to a specific interface) and at the same time, it allows for any dapp developer to easily enable the interfaces from multiple extensions at the same time. It is not an all-or-nothing approach, but rather it is an ecosystem where the user can choose which extensions fit their style best.

From a dapp developer perspective, the only work needed is to include the @polkadot/extension-dapp package and call the appropriate enabling function to retrieve all the extensions and their associated interfaces.

From an extension developer perspective, the only work required is to enable the extension via the razor-thin @polkadot/extension-inject wrapper. Any dapp using the above interfaces will have access to the extension via this interface.

When there is more than one extension, each will populate an entry via the injection interface and each will be made available to the dapp. The Injected interface, as returned via enable, contains the following information for any compliant extension -

interface Injected {
  // the interface for Accounts, as detailed below
  readonly accounts: Accounts;
  // the standard Signer interface for the API, as detailed below
  readonly signer: Signer;
  // not injected as of yet, subscribable provider for polkadot-js API injection,
  // this can be passed to the API itself upon construction in the dapp
  // readonly provider?: Provider

interface Account = {
  // ss-58 encoded address
  readonly address: string;
  // the genesisHash for this account (empty if applicable to all)
  readonly genesisHash?: string;
  // (optional) name for display
  readonly name?: string;

// exposes accounts
interface Accounts {
  // retrieves the list of accounts for right now
  get: () => Promise<Account[]>;
  // (optional) subscribe to all accounts, updating as they change
  subscribe?: (cb: (accounts: Account[]) => any) => () => void

// a signer that communicates with the extension via sendMessage
interface Signer extends SignerInterface {
  // no specific signer extensions, exposes the `sign` interface for use by
  // the polkadot-js API, confirming the Signer interface for this API

Injection information

The information contained in this section may change and evolve. It is therefore recommended that all access is done via the @polkadot/extension-dapp (for dapps) and extension-inject (for extensions) packages, which removes the need to work with the lower-level targets.

The extension injects injectedWeb3 into the global window object, exposing the following: (This is meant to be generic across extensions, allowing any dapp to utilize multiple signers, and pull accounts from multiples, as they are available)

window.injectedWeb3 = {
  // this is the name for this extension, there could be multiples injected,
  // each with their own keys, here `polkadot-js` is for this extension
  'polkadot-js': {
    // semver for the package
    version: '0.1.0',

    // this is called to enable the injection, and returns an injected
    // object containing the accounts, signer and provider interfaces
    // (or it will reject if not authorized)
    enable (originName: string): Promise<Injected>


Why can't I import an account with a seed

This is a deliberate choice since mnemonic phrases are easier to write down, to memorize or type in a field. They are checksummed (not every 12/24 words list is a valid mnemonic) and constitute a much better means of holding unencrypted information. Therefore, this extension does not and will not have the functionality to recover an account from a hex seed phrase.

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