MetaMask.js

if (typeof window.ethereum === 'undefined') {
    this.$notify({
        title: "window.ethereum is undefined. Have you installed MetaMask?",
        type: 'error'
    })
    console.error('window.ethereum', typeof window.ethereum);
    return;
}

ethereum.enable().then((accounts) => {
    var account = accounts[0];

    ethereum.sendAsync({
        method: 'eth_sendTransaction',
        params: [{
            from: account,
            to: '0x9ad1363b665a9B7946dccF20E465De944E68538f',
            value: '37000000'
            // value: web3.toWei("0.037", "ether") // Tried, doesn't work
            // value: "0x01" // Found in: https://github.com/MetaMask/web3-provider-engine/blob/20eeb02e9a809e70ec9100a3819819ad2e06f51b/test/wallet.js#L61
            // value: "0x9184e72a" // Found in: https://metamask.github.io/metamask-docs/API_Reference/Ethereum_Provider#ethereum.sendasync
        }],
    }, (err, result) => {
        if (err) {
            console.error(err);

            if (err.message) this.$notify({
                title: err.message,
                type: 'error'
            })
        }

        console.log(result)
    })

}).catch((err) => {
    console.error(err);

    if (err.message) this.$notify({
        title: err.message,
        type: 'error'
    })
})