Use the spread operator.
data: {
userId: 7,
actionId: 36,
...myCondition && {express: true}
}
Note that if you’re using Flow, that syntax might generate type check errors. You can write the above more explicitly, and less succinctly, as:
data: {
userId: 7,
actionId: 36,
...(myCondition ? {express: true} : {})
}