Access fields from the issue object in Behaviours for Jira Cloud

// Access the context for the UI Modification
const context = await getContext()

// Get the current issue key
const issueKey = context.extension.issue.key;

// Get the current issue object 
const issue = await makeRequest("/rest/api/2/issue/" + issueKey);

// Log out to the browser some field values to show how to get them from the issue.  
// Note you can access any field on an issue through the fields property

console.log("Issue Field Values:")
console.log("Status field: ", issue.body.fields.status)
console.log("Assignee field: ", issue.body.fields.assignee)