参考：https://stackoverflow.com/questions/67597665/how-to-change-network-in-metamask-using-react-js

What if the user doesn't have the required network added? Here is an expanded version which tries to switch, otherwise add the network to MetaMask:

const chainId = 137 // Polygon Mainnet
if (window.ethereum.networkVersion !== chainId) {
try {
await window.ethereum.request({
method: 'wallet_switchEthereumChain',
params: [{ chainId: web3.utils.toHex(chainId) }]
});
} catch (err) {
// This error code indicates that the chain has not been added to MetaMask
if (err.code === 4902) {
await window.ethereum.request({
method: 'wallet_addEthereumChain',
params: [
{
chainName: 'Polygon Mainnet',
chainId: web3.utils.toHex(chainId),
nativeCurrency: { name: 'MATIC', decimals: 18, symbol: 'MATIC' },
rpcUrls: ['https://polygon-rpc.com/']
}
]
});
}
}
}
</div>