With over 10,000 blockchains currently operating, there are endless possibilities for deploying your smart contracts.

For anybody to be able to use your Decentralized Application (DApp), they need to be connected to the blockchain where you've deployed your smart contract.

This article will show you how to prompt your users to switch to your preferred blockchain using JavaScript.

This guide requires that you have the MetaMask extension installed. Also, I assume you have a little bit of experience connecting with MetaMask—perhaps you've previously built a DApp. If you need a quick intro, check out this brilliant piece by MetaMask to get started.

Alright, Let’s dig in!

Step 1 — Check if the User Has MetaMask Installed

The first thing to do is to verify if the user has installed the MetaMask extension.

If they have another wallet installed besides MetaMask, switching networks using the method we are about to learn might not work. So it's a good idea to check first.

Let's check if the ethereum context has been injected into the browser. The code sample below shows how to do this:

const { ethereum } = window;

if (typeof ethereum !== 'undefined' && ethereum.isMetaMask) {  
 console.log("MetaMask is installed")
} else {
  console.log("MetaMask is not installed")

Here's what we're doing:

At const { ethereum } = window; we destructure the ethereum property from the windows object and assign it to a variable of the same name.

If you are unfamiliar with this syntax, destructuring involves simply extracting the content of an object or array and assigning it to a variable. Read up on this piece to learn more about destructuring.

Then we check if ethereum actually does exist using the if statement. Also, in the same condition we want to verify if the wallet installed is MetaMask.

Good! Let's see the next step.

Step 2  — How to Switch the Active Blockchain

Once we have verified that the user has MetaMask installed, the next thing to do is trigger the RPC method for switching the MetaMask active blockchain. The code looks like this:

// MetaMask Docs
try {
  await ethereum.request({
    method: 'wallet_switchEthereumChain',
    params: [{ chainId: '0xf00' }],
} catch (switchError) {
// This error code indicates that the chain has not been added to MetaMask.
  if (switchError.code === 4902) {
  	// Do something

Here's what we are doing:

We invoke the ethereum.request method, passing it an object with two properties.

In the method property, we specify the wallet_switchEthereumChain RPC method, which allows Ethereum applications (DApps) to request that MetaMask switches its active Ethereum chain.

Then, the params property is an array that takes an object with the chain ID of the blockchain to switch to. chainId must be hexadecimal, hence the 0x in the sample code.

We wrap our request in a try/catch block to handle errors.

null is returned if the active chain is switched.

If the requested chain does not exist in the user's wallet, the request throws an error code error.code of  4902. If this happens, you can request to add the chain to the wallet.

You can follow this guide to see how to add a new chain to MetaMask using JavaScript.

Great! That's all it takes to switch the active chain on MetaMask with Javascript.

Let's have a quick demo in the next section.


For this example, let's write a function that, when invoked, will prompt users to switch to the Polygon chain.

const SwitchChainToPolygon = () => {
	const { ethereum } = window;
    if (typeof ethereum !== 'undefined' && ethereum.isMetaMask) return;
    try {
      await ethereum.request({
        method: 'wallet_switchEthereumChain',
        params: [{ chainId: '0x89' }],
    } catch (switchError) {
      if (switchError.code === 4902) {
        // You can make a request to add the chain to wallet here
        console.log('Polygon Chain hasn't been added to the wallet!')

In the function SwitchChainToPolygon above, we destructured ethereum from the windows object, as we learned in Step 1.

Next, we verified whether ethereum does exist or not. If the ethereum is unavailable, that is if MetaMask is not installed, the function will exit/break.

If ethereum exists, we call the ethereum.request method to make an RPC call. For the method property, we give it a value of wallet_switchEthereumChain. For the params, chainId will have the value of 0x89 ( 167 in decimal) which is the chainId for the polygon blockchain.

That's all folks!


In this article, you have learned how to switch blockchains on MetaMask with JavaScript. This will help you provide a frictionless user experience for your users.

Thank you for taking the time to read this. I hope you found it useful. Please feel free to connect and chat with me on Twitter and YouTube. See you soon in my next article!