promise.then()
以下、SalesforceのVisualforceページにて検証
<apex:page>
    <html>
        <head>
        </head>
        <body>
            <script type="text/javascript">
                const promise1 = new Promise((resolve, reject) => {
                resolve('Success!');
                });
                promise1.then((value) => {
                console.log(value);
                // expected output: "Success!"
                });
                
            </script>
        </body>
    </html>
</apex:page>