Skip to main content

Cookbook

A set of code snippets ready to be used.

Get all extensions accounts#

A dapp will not be aware whether or not the user has the extension installed on their browser until the web3Enable function is called. Calling this function returns the amount of extensions installed and for which the user has accepted to share their accounts. Using web3Accounts, you can then retrieve the visible accounts. See below for web3AccountsSubscribe usage.

import { web3Accounts, web3Enable } from '@polkadot/extension-dapp';
// this call fires up the authorization popupconst extensions = await web3Enable('my cool dapp');
if (extensions.length === 0) {    // no extension installed, or the user did not accept the authorization    // in this case we should inform the use and give a link to the extension    return;}
// we are now informed that the user has at least one extension and that we// will be able to show and use accountsconst allAccounts = await web3Accounts();

Sign a message#

Here is an example on how to sign a message with an account that was injected by the extension.

// We arbitraily select the first account returned from the above snippet// `account` is of type InjectedAccountWithMeta const account = allAccount[0];
// to be able to retrieve the signer interface from this account// we can use web3FromSource which will return an InjectedExtension typeconst injector = await web3FromSource(account.meta.source);

// this injector object has a signer and a signRaw method// to be able to sign raw bytesconst signRaw = injector?.signer?.signRaw;
if (!!signRaw) {    // after making sure that signRaw is defined    // we can use it to sign our message    const { signature } = await signRaw({        account.address,        data: stringToHex('message to sign'),        type: 'bytes'    });}

Head to the relevant util-crypto example to see how to verify a signature.

Sign and send a transaction#

The api is able to retrieve the signer when signAndSend is called with the address from an account retrieved from the extension.

// We arbitraily select the first account returned from the above snippet// `account` is of type InjectedAccountWithMeta const account = allAccount[0];
// here we use the api to create a balance transfer to some account of a value of 12344const transferExtrinsic = api.tx.balances.transfer('5C5555yEXUcmEJ5kkcCMvdZjUo7NGJiQJMS7vZXEeoMhj3VQ', 123456)
// to be able to retrieve the signer interface from this account// we can use web3FromSource which will return an InjectedExtension typeconst injector = await web3FromSource(account.meta.source);
// passing the injected account address as the first argument of signAndSend// will allow the api to retrieve the signer and the user will see the extension// popup asking to sign the balance transfer transactiontransferExtrinsic.signAndSend(account.address, { signer: injector.signer }, ({ status }) => {    if (status.isInBlock) {        console.log(`Completed at block hash #${status.asInBlock.toString()}`);    } else {        console.log(`Current status: ${status.type}`);    }}).catch((error: any) => {    console.log(':( transaction failed', error);});

Subscription to extensions' accounts#

Using web3AccountsSubscribe similarly as what we did above with web3Accounts allows to get all injected accounts, in this case though because we use a subscription, we will be aware of any account change.

import { web3AccountsSubscribe, web3Enable } from '@polkadot/extension-dapp';
// this call fires up the authorization popupconst extensions = await web3Enable('my cool dapp');
if (extensions.length === 0) {    // no extension installed, or the user did not accept the authorization    // in this case we should inform the use and give a link to the extension    return;}
// we are now informed that the user has at least one extension and that we// will be able to show and use accountslet unsubscribe; // this is the function of type `() => void` that should be called to unsubscribe
// we subscribe to any account change and log the new list.// note that `web3AccountsSubscribe` returns the function to unsubscribeunsubscribe = await web3AccountsSubscribe(( injectedAccounts ) => {     injectedAccounts.map(( accounts ) => {        console.log(account.address);    }) });
// don't forget to unsubscribe when needed, e.g when unmounting a componentunsubscribe && unsubscribe();