Connect Lamden vault 🔗︎



the following skills are necessary for these tutorials(web): - Experience using the command line - Basic knowledge about JavaScript, React, Git


Here is the completed Git repo for this part

1. Open the starter web project 🔗︎

Clone the exercise repo.

git clone

Open the folder ——— lottery-frontend(Tutorials) in Visual Studio Code


Let's start this project!

npm run start

Open your browser and navigate to http://localhost:3000. You would see an uncompleted Lottery Dapp.


2. Connect Lamden Vault 🔗︎

Open the file src\Components\Layout.jsx. We will complete the function of connecting the Lamden Vault.


Now let us complete the function connect() which will send a connection request by dispatching a "lamdenWalletConnect" event. For more details, click here.

As you can see in the following code, there are two variables AppInfo and Network. AppInfo saves the dapp info and the Network records the Lamden Network info. You can edit them as needed in file src\Constant.js.

const connect = () => {
    const detail = JSON.stringify({
        appName: AppInfo.appName, // dapp name
        version: AppInfo.version, // dapp verision
        logo: AppInfo.logo, // dapp logo
        contractName: Network[process.env.NODE_ENV].contractName, // the contract name you create at tutorial "Write Lottery Contract" 
        networkType: Network[process.env.NODE_ENV].networkType, // Network type

    // Dispatch connection event
    document.dispatchEvent(new CustomEvent('lamdenWalletConnect', {detail}));

It's time to handle the response of the connection request from Lamden Vault.

First we should add a listener to receive the response and call the callback function to handle it. We use addEventListener to add a listener for 'lamdenWalletConnect' event. The callback function handleWalletConnect will be called when the listener receive a message.

Also, don't forget to remove the existing listener to prevent memory leakage.

useEffect(() => {
    document.addEventListener('lamdenWalletConnect', handleWalletConnect);
    return () => {
        document.removeEventListener('lamdenWalletConnect', handleWalletConnect);
}, [])

When we get the response of the connecting request, we should give feedback to users whether the connection is successful. If success, we should update the wallet context.

const handleWalletInfo = (response) => {
    if (response.detail.errors){
        // If an error occurs, a pop-up window will appear
            # 'Wallet Error',
            description: response.detail.errors[0],
            status: 'error',
            duration: 9000,
            position: 'top',
            isClosable: true,
    } else {
        let locked = response.detail.locked;
        let account = !locked && response.detail.wallets.length > 0 ? response.detail.wallets[0] : null;
        // account: Wallet account
        // locked: Whether the Lamden Vault is locked
        // connected: Whether connection is successful
            connected: account ? true : false,

If we want to disconnect from the Lamden vault, just reset the wallet context.

const disconnect = () => {
        connected: false,
        locked: true,
        tauBalance: 0,
        address: null,

3. Test the application 🔗︎

Save the changes in the file src\Components\Layout.jsx and then come back to your browser.

Click the button Connect on the top right-corner of the page.

If your Lamden Vault is locked, you will see:


If your Lamden Vault is unlock, you will see: